Metal oxide semiconductor having epitaxial source drain regions and a method of manufacturing same using dummy gate process

ABSTRACT

A semiconductor device in which sufficient stress can be applied to a channel region due to lattice constant differences.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.14/672,385 filed Mar. 30, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/177,705 filed Feb. 11, 2014, which is acontinuation of U.S. patent application Ser. No. 13/615,799 filed Sep.14, 2012 now U.S. Pat. No. 9,041,058 issued May 26, 2015, which is acontinuation of U.S. patent application Ser. No. 12/518,540, filed Jun.10, 2009, now U.S. Pat. No. 8,361,850 issued on Jan. 29, 2013, which isthe Section 371 National Stage of PCT/JP2007/073689, filed Dec. 7, 2007,the entireties of which are incorporated herein by reference to theextent permitted by law. The present application claims priority to andcontains subject matter related to Japanese Patent Application No. JP2006-333087 filed in the Japanese Patent Office on Dec. 11, 2006 andJapanese Patent Application No. JP 2007-308597 filed in the JapanesePatent Office on Nov. 29, 2007, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method for manufacturing asemiconductor device and a semiconductor device, and particularly to aMOS (Metal Oxide Semiconductor) field effect transistor.

BACKGROUND ART

Along with the advancing of the generation of transistors, scaling byminiaturization is also being advanced constantly. On the roadmap of theITRS (International Technology Roadmap for Semiconductor), it isexpected that a gate length (Lg) of 20 nm or smaller will be achieved intransistors called the 32-nm node. The scaling needs to be advanced forLg as well as for other parameters such as the equivalent oxidethickness (EOT) of a gate insulating film and the depth (Xj) ofdiffusion layers.

The above-described scaling of the EOT is effective for ensuring of thedriving capability (Ids). However, the physical thickness of a silicondioxide (SiO₂)-based insulating film, which is used as a gate insulatingfilm in related arts, is about to reach the limit, and therefore thetechnical difficulty in suppression of gate leakage is becomingparticularly higher. This causes slowdown in the progression of thescaling after the generation of the 90-nm node. As a solution thereto,studies are being made on suppression of the depletion of a gateelectrode through introduction of a High-k insulating film instead ofthe above-described SiO₂-based insulating film and through introductionof a metal gate electrode instead of a poly-silicon (Poly-Si) gateelectrode.

As the material of the above-described metal gate electrode, tungsten(W), titanium (Ti), hafnium (Hf), ruthenium (Ru), iridium (Ir), or thelike is used. These metals are highly-reactive materials. Therefore,when being subjected to high-temperature heat treatment, these metalsreact with a gate insulating film and so on, which causes thedeterioration of the film quality of the gate insulating film.Consequently, it is desirable that high-temperature heat treatment benot performed after formation of the metal gate electrode. As one methodto realize this desire, a dummy gate process (damascene gate process)has been proposed (refer to e.g. Japanese Patent Laid-open No.2000-315789 and Japanese Patent Laid-open No. 2005-26707).

The dummy gate process has the following process flow. Specifically,initially a dummy gate is formed on a silicon substrate by using Poly-Sior the like, followed by formation of diffusion layers such assource/drain regions and extension regions. Thereafter, an interlayerinsulating film is formed, and then the upper face of the dummy gate isexposed by a chemical mechanical polishing (CMP) method. Subsequently,the dummy gate is removed, so that a trench (recess) for burying a gatematerial therein is formed in a self-aligned manner. If after theformation of the trench, a gate insulating film for a transistor isformed and immediately thereafter a metal gate electrode is buried inthe trench, heat treatment required for activation of the diffusionlayers is unnecessary after the formation of the metal gate electrode,and hence subsequent processing steps can be carried out at a lowtemperature.

Meanwhile, a large number of techniques that allow enhancement in thedriving capability without relying on the scaling have also beenproposed in recent years. In these techniques, the driving capability isenhanced by applying stress to a channel region to thereby increase themobility of electrons and holes (refer to e.g. T. Ghani et al.,International Electron Devices Meeting Technical Digest, 2003, p. 987).

A description will be made below about an example in which this mobilityenhancement technique is applied to a method for manufacturing a p-typefield effect transistor (PMOS transistor) by use of the sectional viewsof FIGS. 21 and 22, which show manufacturing steps.

Referring initially to (a) of FIG. 21, element isolation regions (notshown) are formed on the surface side of a silicon (Si) substrate 101.Subsequently, over the Si substrate 101, a gate electrode 103 composedof Poly-Si is pattern-formed with the intermediary of a gate insulatingfilm 102 composed of SiO₂. At this time, the respective material filmsfor forming the gate insulating film 102 and the gate electrode 103, anda hard mask 104 formed of a silicon nitride (SiN) film are stacked overthe Si substrate 101, and then the hard mask 104 and the gate electrode103 are pattern-etched.

Subsequently, as shown in (b) of FIG. 21, offset spacers 105 formed of aSiN film are formed on both the sides of the gate insulating film 102,the gate electrode 103, and the hard mask 104. Referring next to (c) ofFIG. 21, sidewalls 106 composed of SiO₂ are formed on both the sides ofthe gate insulating film 102, the gate electrode 103, and the hard mask104, for which the offset spacers 105 have been provided.

Subsequently, as shown in (d) of FIG. 21, by using the gate electrode103 as a mask, for which the hard mask 104 has been provided thereon andthe sidewalls 106 have been provided on both the sides thereof with theintermediary of the offset spacers 105, the Si substrate 101 ispartially removed by etching, i.e., so-called recess etching isperformed, to thereby form recess regions 107. Thereafter, a naturaloxide film on the surface of the Si substrate 101 is removed by cleaningtreatment with a dilute hydrofluoric acid.

Subsequently, as shown in (e) of FIG. 22, on the recess regions 107,i.e., on the surface of the partially etched part of the Si substrate101, mixed crystal layers 108 formed of a silicon germanium (SiGe) layerdoped with a p-type impurity are epitaxially grown. Thereby, these mixedcrystal layers 108 will serve as the source/drain regions, and theregion in the Si substrate 101 between the source/drain regions anddirectly beneath the gate electrode 103 will serve as a channel regionCh. The mixed crystal layers 108 are composed of Si and Ge having alattice constant larger than that of Si. Therefore, compressive stressis applied to the channel region Ch interposed between the mixed crystallayers 108, so that strain arises in the channel region Ch.

Thereafter, as shown in (f) of FIG. 22, the sidewalls 106 (seeabove-described (e) of FIG. 22) are removed, so that the surface of theSi substrate 101 on both the sides of the gate electrode 103 providedwith the offset spacers 105 is exposed.

Referring next to (g) of FIG. 22, ion implantation is performed for theSi substrate 101 on both the sides of the gate electrode 103 providedwith the offset spacers 105 by using the offset spacers 105 and the hardmask 104 as the mask, to thereby form extension regions 109.

Subsequently, as shown in (h) of FIG. 22, sidewalls 110 composed of SiNare newly formed on both the sides of the offset spacers 105.Thereafter, by wet etching, the hard mask 104 (see above-described (g)of FIG. 22) is removed to expose the surface of the gate electrode 103,and a natural oxide film on the surfaces of the mixed crystal layers 108is removed.

Subsequently, a refractory metal film such as a nickel film is depositedacross the entire surface of the Si substrate 101, including on themixed crystal layers 108, in such a manner as to cover the gateelectrode 103, for which the sidewalls 110 have been provided on boththe sides thereof with the intermediary of the offset spacers 105.Thereafter, heat treatment is performed to thereby turn the surfacesides of the gate electrode 103 and the mixed crystal layers 108 into asilicide, so that silicide layers 111 composed of a nickel silicide areformed. This decreases the resistance of the surface side of thesource/drain regions, and thus reduces the contact resistance.

In the above-described manner, by straining the channel region Chthrough application of compressive stress to the channel region Ch fromthe mixed crystal layers 108, a PMOS transistor having sufficiently-highcarrier mobility can be obtained.

In addition, although not shown in the drawings, in the case of formingan n-type field effect transistor (for example, an NMOS transistor), asilicon carbide (SiC) layer composed of Si and carbon (C) having alattice constant smaller than that of Si is epitaxially grown as themixed crystal layers 108 on the recess regions 107, to thereby applytensile stress to the channel region Ch. This strains the channel regionCh, which can provide an NMOS transistor having sufficiently-highcarrier mobility.

Furthermore, there has also been disclosed a method in which theabove-described damascene gate process is used and a SiGe layer isformed on recess regions on both the sides of a gate electrode by aselective CVD (Chemical Vapor Deposition) method (refer to e.g. JapanesePatent Laid-open No. 2004-31753).

However, in the above-described method for manufacturing the PMOSdescribed by using FIGS. 21 and 22, referring to the plan view of (a) ofFIG. 23 and the sectional view of (b) of FIG. 23, compressive stress(arrowheads A) is applied to the channel region Ch from the mixedcrystal layers 108 formed of a SiGe layer. By this stress, in the xyplane, escaping force (arrowheads B) works in the directionsperpendicular to arrowheads A. In addition, along the direction of thenormal of the Si substrate 101 (z direction), escaping force (arrowheadsC) works toward the outside of the Si substrate 101. Thus, if the gateelectrode 103 composed of Poly-Si exists over the channel region Ch inthe Si substrate 101, the escaping force (arrowheads C) toward theoutside of the Si substrate 101 is suppressed by counteraction(arrowheads D) from the gate electrode 103. This precludes sufficientapplication of compressive force to the channel region Ch, and hencesuppresses enhancement in the carrier mobility.

Furthermore, also in the above-described method for manufacturing thePMOS, referring to the plan view of (a) of FIG. 24 and the sectionalview of (b) of FIG. 24, compressive stress (arrowheads A′) is applied tothe channel region Ch from mixed crystal layers 108′ formed of a SiClayer. By this stress, in the xy plane, escaping force (arrowheads B′)works in the directions perpendicular to arrowheads A′. In addition,along the direction of the normal of the Si substrate 101 (z direction),escaping force (arrowheads C′) works toward the inside of the Sisubstrate 101. Thus, if the gate electrode 103 composed of Poly-Siexists over the channel region Ch in the Si substrate 101, the escapingforce (arrowheads C′) toward the inside of the Si substrate 101 issuppressed by counteraction (arrowheads D′) from the gate electrode 103.This precludes sufficient application of compressive force to thechannel region Ch, and hence suppresses enhancement in the carriermobility.

Furthermore, to enhance the effect of the stress, it is effective toincrease the Ge concentration in the mixed crystal layers 108 formed ofa SiGe layer in the PMOS transistor and increase the C concentration inthe mixed crystal layers 108′ composed of SiC in the NMOS transistor.However, if the germanium (Ge) concentration or the carbon (C)concentration is too high, defects will occur at the interface betweenthe Si substrate 101 and the mixed crystal layers 108 or the mixedcrystal layers 108′. This will result in the occurrence of problems suchas the lowering of the stress and increase in junction leakage.

On the other hand, in the method described in Japanese Patent Laid-openNo. 2004-31753, in which a SiGe layer is formed on recess regions by aselective CVD method, compressive stress to a channel region does notarise because the SiGe layer is formed by the selective CVD method. Inaddition, the SiGe layer is formed also in an NMOS region, and thustensile stress to a channel region does not arise.

Accordingly, it is an object of the present invention to provide amethod for manufacturing a semiconductor device and a semiconductordevice, each allowing prevention of crystal defects due to the existenceof a high concentration of atoms having a lattice constant differentfrom that of Si in a mixed crystal layer, and each permitting sufficientapplication of stress to a channel region.

DISCLOSURE OF INVENTION

To achieve the above-described objects, a method for manufacturing asemiconductor device (a first manufacturing method) according to thepresent invention is characterized by that the following steps aresequentially carried out. Initially, in a first step, a dummy gateelectrode is formed over a silicon substrate. Subsequently, in a secondstep, a recess region is formed by partially removing the siliconsubstrate through recess etching in which the dummy gate electrode isused as a mask. Subsequently, in a third step, a mixed crystal layerthat is composed of silicon and an atom having a lattice constantdifferent from that of silicon is epitaxially grown on the surface ofthe recess region. Subsequently, in a fourth step, an insulating film isformed on the mixed crystal layer in such a way that the dummy gateelectrode is covered by the insulating film, and the insulating film isremoved until the surface of the dummy gate electrode is exposed.Thereafter, in a fifth step, a recess is formed in the insulating filmby removing the exposed dummy gate electrode. Subsequently, in a sixthstep, a gate electrode is formed in the recess with the intermediary ofa gate insulating film.

In this method for manufacturing a semiconductor device (the firstmanufacturing method), the recess is formed by removing the exposeddummy gate electrode. Thus, it is avoided that stress applied from themixed crystal layer to a channel region directly beneath the dummy gateelectrode is suppressed by counteraction from the dummy gate electrode.

Furthermore, thereafter, the gate electrode is so formed in the recesswith the intermediary of the gate insulating film that the stress stateis kept. This allows effective stress application to the channel region,and hence can strain the channel region to thereby enhance the carriermobility.

In addition, this effective stress application to the channel regionmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layer. This feature can surely prevent crystal defectsattributed to the existence of a high concentration of the atoms in themixed crystal layer.

A method for manufacturing a semiconductor device (a secondmanufacturing method) according to the present invention ischaracterized by including: a first step of forming a dummy gateelectrode over a silicon substrate with intermediary of a gateinsulating film; a second step of forming a recess region by partiallyremoving the silicon substrate through recess etching in which the dummygate electrode is used as a mask; a third step of epitaxially growing ona surface of the recess region a mixed crystal layer that is composed ofsilicon and an atom having a lattice constant different from a latticeconstant of silicon; a fourth step of forming an insulating film on themixed crystal layer in such a way that the dummy gate electrode iscovered, and removing the insulating film until a surface of the dummygate electrode is exposed; a fifth step of forming a recess that exposesthe gate insulating film in the insulating film by removing the exposeddummy gate electrode; and forming a gate electrode in the recess withintermediary of a gate insulating film.

A method for manufacturing a semiconductor device (a third manufacturingmethod) according to the present invention is characterized byincluding: a first step of forming a dummy gate electrode over a siliconsubstrate with intermediary of a gate insulating film and a cap filmprovided on the gate insulating film; a second step of forming a recessregion by digging down the silicon substrate by recess etching in whichthe dummy gate electrode is used as a mask; a third step of epitaxiallygrowing, on a surface of the recess region, a mixed crystal layer thatis composed of silicon and an atom different from silicon in a latticeconstant; a fourth step of forming an insulating film on the mixedcrystal layer in such a state as to cover the dummy gate electrode andremoving the insulating film until a surface of the dummy gate electrodeis exposed; a fifth step of forming a recess that exposes the cap filmin the insulating film by removing the dummy gate electrode that isexposed and the cap film; and a sixth step of forming a gate electrodein the recess with intermediary of the gate insulating film and the capfilm.

A method for manufacturing a semiconductor device (a fourthmanufacturing method) according to the present invention ischaracterized by including: a first step of forming a dummy gateelectrode over a silicon substrate with intermediary of a gateinsulating film and a cap film provided on the gate insulating film; asecond step of forming a recess region by digging down the siliconsubstrate by recess etching in which the dummy gate electrode is used asa mask; a third step of epitaxially growing, on a surface of the recessregion, a mixed crystal layer that is composed of silicon and an atomdifferent from silicon in a lattice constant; a fourth step of formingan insulating film on the mixed crystal layer in such a state as tocover the dummy gate electrode and removing the insulating film until asurface of the dummy gate electrode is exposed; a fifth step of forminga recess that exposes the cap film in the insulating film by removingthe dummy gate electrode that is exposed; a fifth step of forming ametal film that is to be reacted with the cap film at least on a bottomof the recess; a sixth step of forming a film that controls a workfunction by reacting the metal film with the cap film; and a seventhstep of forming a gate electrode in the recess with intermediary of thegate insulating film and the film that controls a work function.

According to the above-described method for manufacturing asemiconductor device (the second to fourth manufacturing method), therecess is formed by removing the exposed dummy gate electrode. Thus, itis avoided that stress applied from the mixed crystal layers to thechannel region directly beneath the dummy gate electrode is suppressedby counteraction from the dummy gate electrode. Furthermore, thereafter,the gate electrode is so formed on the gate insulating film in therecess that the stress state is kept. This allows effective stressapplication to the channel region, and hence can strain the channelregion to thereby enhance the carrier mobility.

In addition, this effective stress application to the channel regionmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layers.

This feature can surely prevent crystal defects attributed to theexistence of a high concentration of the atoms in the mixed crystallayers.

Furthermore, the gate insulating film is not formed on the sidewall ofthe gate electrode. Therefore, the parasitic capacitance between thesidewall of the gate electrode and the mixed crystal layers to serve asthe source and drain becomes lower with respect to the fringecapacitance of the gate electrode. This can enhance the operating speedof the MOS transistor compared with the case in which the gateinsulating film is formed on the sidewall of the gate electrode.

A semiconductor device according to the present invention is thesemiconductor device including a gate electrode configured to beprovided over a silicon substrate with the intermediary of a gateinsulating film in such a way that the sidewall of the gate electrode iscovered by the gate insulating film, and a mixed crystal layerconfigured to be provided on a recess region obtained through partialremoval of the silicon substrate on both the sides of the gate electrodeand be composed of silicon and an atom having a lattice constantdifferent from that of silicon.

Such a semiconductor device is manufacturing by the above-describedmanufacturing method. Therefore, stress is effectively applied to theabove-described channel region. This feature can strain the channelregion for enhancement in the carrier mobility, and can surely preventcrystal defects attributed to the existence of a high concentration ofatoms having a lattice constant different from that of Si in the mixedcrystal layer.

As described above, the method for manufacturing a semiconductor deviceand the semiconductor device according to the embodiments of the presentinvention allow enhancement in the carrier mobility and ensuredprevention of crystal defects in a mixed crystal layer. Consequently,transistor characteristics such as the on/off ratio can be enhanced.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a)-1(d) are sectional views (part one) for explainingmanufacturing steps of a method for manufacturing a semiconductor deviceaccording to a first embodiment of the present invention.

FIGS. 2(e)-2(h) are sectional views (part two) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the first embodiment of the present invention.

FIGS. 3(i)-3(l) are sectional views (part three) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the first embodiment of the present invention.

FIGS. 4(m)-4(o) are sectional views (part four) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the first embodiment of the present invention.

FIGS. 5A(1)-5A(2) show the results of simulation of stress applied to achannel region.

FIG. 5B is a graph showing results of simulation of stress applied to achannel region.

FIG. 5C is another graph showing results of simulation of stress appliedto a channel region.

FIG. 6 is a graph showing variation in stress applied to a channelregion when the germanium concentration is changed.

FIG. 7 is a graph showing the relationships between the on-current andthe off-current.

FIG. 8 is a graph showing the results of measurement of variation in theon-resistance value when the gate length is changed.

FIGS. 9(a)-9(d) are sectional views (part one) for explainingmanufacturing steps of a method for manufacturing a semiconductor deviceaccording to a second embodiment of the present invention.

FIGS. 10(e)-10(h) are sectional views (part two) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the second embodiment of the present invention.

FIGS. 11(i)-11(k) are sectional views (part three) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the second embodiment of the present invention.

FIGS. 12(l)-12(n) are sectional views (part four) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the second embodiment of the present invention.

FIGS. 13(a)-13(d) are sectional views (part one) for explainingmanufacturing steps of a method for manufacturing a semiconductor deviceaccording to a third embodiment of the present invention.

FIGS. 14(e)-14(h) are sectional views (part two) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the third embodiment of the present invention.

FIGS. 15(i)-15(l) are sectional views (part three) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the third embodiment of the present invention.

FIGS. 16(m)-16(o) are sectional views (part four) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the third embodiment of the present invention.

FIGS. 17(a)-17(b) are sectional views (part one) for explainingmanufacturing steps of a method for manufacturing a semiconductor deviceaccording to a fourth embodiment of the present invention.

FIGS. 18(c)-18(d) are sectional views (part two) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the fourth embodiment of the present invention.

FIGS. 19(a)-19(b) are sectional views (part one) for explainingmanufacturing steps of a method for manufacturing a semiconductor deviceaccording to a fifth embodiment of the present invention.

FIGS. 20(c) and 20(d) are sectional views (part two) for explainingmanufacturing steps of the method for manufacturing a semiconductordevice according to the fifth embodiment of the present invention.

FIGS. 21(a)-21(d) are sectional views (part one) for explainingmanufacturing steps of a related method for manufacturing asemiconductor device.

FIGS. 22(e)-22(h) are sectional views (part two) for explainingmanufacturing steps of the related method for manufacturing asemiconductor device.

FIGS. 23(a) and 23(b) are plan view (a) and sectional view (b),respectively for explaining problems in the related method formanufacturing a semiconductor device (PMOS transistor).

FIGS. 24(a) and 24(b) are plan view (a) and sectional view (b),respectively, for explaining problems in the existing method formanufacturing a semiconductor device (NMOS transistor).

BEST MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail belowbased on the drawings. However, in the description of the embodiment,the configuration of a semiconductor device will be explained based onthe order of manufacturing steps thereof.

First Embodiment

As one example of a method for manufacturing a semiconductor deviceaccording to the embodiment of the present invention, a method formanufacturing a PMOS in a CMOS (Complementary Metal Oxide Semiconductor)will be described below by using the sectional views of FIGS. 1 to 4,which show manufacturing steps.

Referring initially to (a) of FIG. 1, element isolation regions (notshown) are formed on the surface side of a silicon (Si) substrate 1 byusing STI (Shallow Trench Isolation) or another method.

Subsequently, on the surface of the silicon substrate 1, a silicondioxide (SiO₂) film is deposited by e.g. oxidation as an anti-channelingprotective film used for ion implantation of an impurity into thesilicon substrate 1.

Thereafter, impurities are introduced by ion implantation for an NMOStransistor region and PMOS transistor region separately, for elementisolation and threshold value regulation.

Subsequently, the above-described silicon dioxide film is removed toexpose the surface of the silicon substrate 1, and then a dummy gateinsulating film 2 composed of e.g. silicon dioxide is formed to athickness of about 1 nm to 3 nm.

Subsequently, a dummy gate electrode film (not shown) composed ofPoly-Si is deposited by e.g. a CVD method to a thickness of about 100 nmto 200 nm. Next, by e.g. a CVD method, a SiN film that will serve as ahard mask is deposited on the dummy gate electrode film to a thicknessof about 30 nm to 100 nm. Subsequently, resist is applied on the SiNfilm, and then this resist is patterned by optical lithography (KrF,ArF, F₂) or electron beam (EB) lithography, to thereby form a resistpattern having a gate electrode pattern.

Subsequently, a hard mask 4 is formed by processing the above-describedsilicon nitride film through dry etching in which this resist pattern isused as the mask. At this time, the hard mask 4 is often subjected tothinning and trimming so as to have a line width smaller than that ofthe resist pattern so that a small gate electrode pattern can beobtained.

Thereafter, the above-described resist pattern is removed, and then dryetching for the dummy gate electrode film is performed by using the hardmask 4 as the mask, to thereby form a dummy gate electrode 3 composed ofPoly-Si.

Thereafter, the resist pattern is removed. In this post treatment, thedummy gate insulating film 2 covering the surface of the siliconsubstrate 1 is removed except for the partial portion under the dummygate electrode 3.

It is to be noted that, although it is described that the dummy gateelectrode 3 is formed by using Poly-Si in the present example, amorphoussilicon may be used as the material of the dummy gate electrode 3.

Furthermore, for the hard mask 4, an insulating film other than the SiNfilm may be used.

In addition, if the above-described dummy gate electrode 3 can be etchedselectively with respect to the silicon substrate 1, the above-describeddummy gate insulating film 2 does not have to be formed.

Referring next to (b) of FIG. 1, offset spacers 5 composed of e.g.silicon nitride (SiN) are formed to a thickness of 1 nm to 10 nm on thesidewalls of the dummy gate insulating film 2, the dummy gate electrode3, and the hard mask 4.

Subsequently, as shown in (c) of FIG. 1, dummy sidewalls 6 composed ofe.g. silicon dioxide (SiO₂) are formed on both the sides of the dummygate insulating film 2, the dummy gate electrode 3, and the hard mask 4,for which the offset spacers 5 have been provided.

The dummy sidewalls 6 will be removed by etching selectively withrespect to the offset spacers 5 in a later step. Therefore, it ispreferable that the dummy sidewalls 6 be formed by using a materialwhich can take etching selection ratio with respect to the material ofthe offset spacers 5.

Referring next to (d) of FIG. 1, recess etching for partially etchingthe silicon substrate 1 is performed by using the hard mask 4 on thedummy gate electrode 3 and the dummy sidewalls 6 as the mask, to therebyform recess regions 7 with a depth of about 50 nm to 100 nm. Throughthis recess etching, only the recess regions 7 for one of an NMOS andPMOS are formed in some cases, and the recess regions 7 are sequentiallyformed for both an NMOS and PMOS in other cases.

It is to be noted that, although it is described that the recess etchingis performed in the state in which the dummy sidewalls 6 have beenprovided in the present example, the present invention can be appliedalso to an example in which the recess etching is performed without theprovision of the dummy sidewalls 6.

Referring next to (e) of FIG. 2, on the surfaces of the recess regions7, i.e., on the surface of the partially etched part of the siliconsubstrate 1, mixed crystal layers 8 composed of Si and atoms having alattice constant different from that of Si are epitaxially grown. Atthis time, at the PMOS transistor side, a silicon germanium (hereinafterreferred to as SiGe) layer composed of silicon (Si) and germanium (Ge)having a lattice constant larger than that of silicon (Si) isepitaxially grown as the mixed crystal layers 8. This SiGe layer willfunction as source/drain regions through introduction of an impuritytherein. Here, simultaneously with the epitaxial growth of the SiGelayer, a p-type impurity such as boron (B) is introduced with aconcentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³. Thereby, the region in thesilicon substrate 1 between the mixed crystal layers 8 and directlybeneath the dummy gate electrode 3 will function as a channel region,and compressive stress (arrowheads A) is applied to the channel regionfrom the mixed crystal layers 8. Thus, as described above by using FIG.23 about a related art, escaping force (arrowheads C) works along thedirection of the normal of the silicon substrate 1 toward the outside ofthe silicon substrate 1. However, this escaping force is suppressed bycounteraction (arrowheads D) from the dummy gate electrode 3, whichresults in the state in which the application of the compressive stressis suppressed.

For effective stress application to the channel region, it is preferablethat the mixed crystal layers 8 be so formed as to protrude from thesurface of the silicon substrate 1. Furthermore, the Ge concentration inthe SiGe layer of the mixed crystal layers 8 is set to a value in aconcentration range of 15 atm % to 20 atm %, in order to prevent crystaldefects due to the existence of a high concentration of Ge in the SiGelayer and effectively apply stress to the channel region.

On the other hand, at an NMOS transistor side, a silicon carbide (SiC)layer composed of silicon (Si) and carbon (C) having a lattice constantsmaller than that of Si is epitaxially grown as the above-describedmixed crystal layers 8, although not shown in the drawings.Simultaneously with the epitaxial growth of the silicon carbide layer,an n-type impurity such as arsenic (As) or phosphorous (P) is introducedwith a concentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³. Here, the Cconcentration in the SiC layer of the mixed crystal layers 8 is set to avalue in a concentration range of 0.5 atm % to 1.5 atm %, in order toprevent crystal defects due to the existence of a high concentration ofcarbon (C) in the silicon carbide layer and effectively apply stress tothe channel region.

It is to be noted that, also in the NMOS transistor side, as describedabove by using FIG. 24 about the related art, escaping force issuppressed by counteraction from the dummy gate electrode 3, whichresults in the state in which the application of the tensile stress issuppressed.

It is to be noted that, although it is described that the mixed crystallayers 8 are epitaxially grown simultaneously with impurity introductionin the present example, an impurity may be introduced by ionimplantation in a step subsequent to the epitaxial growth of the mixedcrystal layers 8 performed without impurity introduction.

The epitaxial growth of the mixed crystal layers 8 for the respectiveelement regions is performed in such a way that the NMOS transistorregion is covered by a protective film such as resist in formation ofthe mixed crystal layers 8 for the PMOS transistor region, and isperformed in such a way that the PMOS transistor region is covered by aprotective film such as resist in formation of the mixed crystal layers8 for the NMOS transistor region.

Referring next to (f) of FIG. 2, the dummy sidewalls 6 (seeabove-described (e) of FIG. 2) are removed by e.g. wet etching tothereby expose the surfaces of the offset spacers 5 and the siliconsubstrate 1.

Subsequently, as shown in (g) of FIG. 2, a p-type impurity such as boronions (B⁺) or indium ions (In⁺) is introduced into the PMOS transistorside by e.g. ion implantation, to thereby form shallow-junctionextension regions 9 on the surface side of the silicon substrate 1 onboth the sides of the offset spacers 5.

At this time, this ion implantation is performed with ion energy of 100eV to 300 eV and a dosage of 5×10¹⁴/cm² to 2×10¹⁵/cm². On the otherhand, also in the NMOS transistor side, arsenic ions (As⁺) orphosphorous ions (P⁺) are introduced with this implantation condition.

It is to be noted that the ion implantation into the respective elementregions is performed in such a way that the NMOS transistor region iscovered by a protective film such as resist in ion implantation into thePMOS transistor region, and is performed in such a way that the PMOStransistor region is covered by a protective film such as resist in ionimplantation into the NMOS transistor region.

Thereafter, as shown in (h) of FIG. 2, sidewalls 10 composed of e.g.silicon nitride are formed again on both the sides of the offset spacers5.

Subsequently, by ion implantation, an impurity is introduced into thesurfaces of the mixed crystal layers 8 by using the hard mask 4 and thesidewalls 10 as the mask. The purpose of this ion implantation is toreduce the contact resistance of a silicide layer that will be formed onthe surfaces of the mixed crystal layers 8 in a later step.

Subsequently, a refractory metal film (not shown) is formed by e.g.sputtering across the entire surface of the silicon substrate 1,including on the mixed crystal layers 8, in such a manner as to coverthe dummy gate electrode 3, for which the hard mask 4 and the sidewalls10 have been provided. As the refractory metal, cobalt (Co), nickel(Ni), platinum (Pt), or a compound of these metals is used.

Subsequently, the silicon substrate 1 is heated to thereby turn thesurface side of the mixed crystal layers 8 into a silicide, so thatsilicide layers 11 are formed.

Thereafter, the unreacted refractory metal film remaining on the elementisolation regions (not shown) and the sidewalls 10 is selectivelyremoved.

Subsequently, as shown in (i) of FIG. 3, an interlayer insulating film12 composed of e.g. silicon dioxide (SiO₂) is formed across the entiresurface of the Si substrate 1, including on the silicide layers 11, insuch a manner as to cover the dummy gate electrode 3, for which the hardmask 4 and the sidewalls 10 have been provided.

Thereafter, as shown in (j) of FIG. 3, the interlayer insulating film 12and the hard mask 4 (see above-described (i) of FIG. 3) are removed by aCMP method until the surface of the dummy gate electrode 3 is exposed.

Subsequently, as shown in (k) of FIG. 3, the dummy gate electrode 3 (seeabove-described (j) of FIG. 3) and the dummy gate insulating film 2 (seeabove-described (j) of FIG. 3) are selectively removed by dry etching,so that a recess 13 is formed.

Thereby, it is avoided in the PMOS transistor that the stress(arrowheads A) applied from the mixed crystal layers 8 to the channelregion Ch directly beneath the dummy gate electrode 3 is suppressed bycounteraction from the dummy gate electrode 3. Thus, the compressivestress to the channel region Ch is increased. Also in the NMOStransistor, the tensile stress to the channel region is increasedsimilarly.

Subsequently, heat treatment is performed for the silicon substrate 1,from which the dummy gate electrode 3 has been removed, at a temperatureof 500° C. to 700° C. for ten seconds to several minutes.

This further increases the stress to the channel region Ch from themixed crystal layers 8.

Subsequently, as shown in (1) of FIG. 3, by e.g. a CVD method, an ALD(Atomic Layer Deposition) method, or a PVD (physical vapor deposition)method, a gate insulating film 14 formed of a High-k film (hereinafterreferred to as high dielectric insulating film) having a dielectricconstant higher than that of silicon dioxide (SiO₂), such as a hafniumoxide (HfO₂) film, is so deposited on the interlayer insulating film 12as to cover the inner wall of the recess 13.

Thereafter, heat treatment at a temperature of 400° C. to 700° C. isperformed to improve the quality of the gate insulating film 14.

It is to be noted that this heat treatment may serve also as theabove-described heat treatment for increasing the stress to the channelregion Ch.

Although it is described that the gate insulating film 14 is so formedas to cover the inner wall of the recess 13 in the present example, thegate insulating film 14 formed of a silicon dioxide (SiO₂) film may beformed by thermal oxidation on the surface of the silicon substrate 1exposed at the bottom of the recess 13 for example. Alternatively, thegate insulating film 14 formed of a silicon oxynitride (SiON) film maybe formed through nitridation of the surface of the silicon dioxide filmformed by the thermal oxidation. In these cases, the gate insulatingfilm 14 is not formed on the sidewall of the recess 13.

Furthermore, the above-described high dielectric insulating film canemploy a metal oxide, a metal silicate, a metal oxynitride, or anitrided metal silicate of one kind of metal selected from hafnium (Hf),lanthanum (La), aluminum (Al), zirconium (Zn), and tantalum (Ta). Forexample, any of the following materials can be used: metal oxides suchas hafnium oxide (HfO₂), aluminum oxide (Al₂O₃), and lanthanum oxide(La₂O₃); metal oxynitrides such as hafnium oxynitride (HfON) andaluminum oxynitride (AlON); metal silicates such as hafnium silicate(HfSiO); and nitrided metal silicates such as nitrided hafnium silicate(HfSiON).

Furthermore, as one example, the above-described gate insulating film 14may be a component obtained by stacking the above-described highdielectric insulating film on a silicon-based insulating film such as asilicon dioxide film or a silicon nitride film.

Referring next to (m) of FIG. 4, by e.g. a CVD method, an ALD method ora PVD method, a gate electrode film 15′ composed of e.g. titaniumnitride (TiN) is so formed on the gate insulating film 14 as to fill therecess 13, in which the gate insulating film 14 has been provided. Asthe material of the gate electrode film 15′, a metal such as titanium(Ti), ruthenium (Ru), hafnium (Hf), iridium (Ir), tungsten (W),molybdenum (Mo), lanthanum (La), or nickel (Ni), or a metal compoundsuch as a Si compound or nitrogen (N) compound of any of these metals isused. This can prevent the depletion of the gate electrode compared withthe case of employing a gate electrode composed of poly-silicon(Poly-Si).

However, the embodiment of the present invention can be applied also tothe case of employing Poly-Si for the gate electrode film 15′.

In the deposition of the gate insulating film 14 and the gate electrodefilm 15′, the deposition condition is so controlled that the state inwhich the stress is applied from the mixed crystal layers 8 to thechannel region Ch can be kept. Specifically, the pressure, power, gasflow rate, or temperature in the film deposition is controlled.

Referring next to (n) of FIG. 4, the gate electrode film 15′ (seeabove-described (m) of FIG. 4) and the gate insulating film 14 areremoved by e.g. a CMP method until the surface of the interlayerinsulating film 12 is exposed, to thereby form a gate electrode 15 inthe recess 13 with the intermediary of the gate insulating film 14.

Through the above-described steps, a CMOSFET is formed.

Thereafter, an interlayer insulating film 16 is further formed on theinterlayer insulating film 12, including on the gate electrode 15, andcontacts and metal interconnects are formed, so that the semiconductordevice is fabricated.

According to such a method for manufacturing a semiconductor device anda semiconductor device obtained by this method, the recess 13 is formedby removing the dummy gate electrode 3 and the dummy gate insulatingfilm 2. Thus, it is avoided that stress applied from the mixed crystallayers 8 to the channel region Ch directly beneath the dummy gateelectrode 3 is suppressed by counteraction from the dummy gate electrode3. Thereafter, the gate electrode 15 is so formed in the recess 13 withthe intermediary of the gate insulating film 14 that the stress state iskept. This allows effective stress application to the channel region Ch,and hence can strain the channel region Ch to thereby enhance thecarrier mobility.

In addition, this effective stress application to the channel region Chmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layers 8. This feature can surely prevent crystal defectsattributed to the existence of a high concentration of theabove-described atoms in the mixed crystal layers 8.

Consequently, characteristics of the transistor can be enhanced.

Here, FIGS. 5A-5C show the results of simulation of the stress appliedto the region in the silicon substrate 1 between the mixed crystallayers 8 and directly beneath the dummy gate electrode 3, in the statein which the dummy gate electrode 3 exists described by using (e) ofFIG. 2 and in the state in which the dummy gate electrode 3 does notexist described by using (k) of FIG. 3.

In the distribution maps shown in FIGS. 5A(1) and 5A(2), a darker colorindicates application of more stress. Therefore, it was confirmed fromthe maps that more stress is applied to the region serving as a channelin the state in which the dummy gate electrode 3 is absent.

In addition, FIG. 5B is a graph arising from quantification of theresults of FIG. 5A, and FIG. 5C is a graph showing the result ofsimulation on variation in the stress across the depth direction of thesilicon substrate 1. These graphs also indicate that more stress isapplied to the region serving as a channel in the state in which thedummy gate electrode 3 is absent.

FIG. 6 shows the result of simulation on comparison of variation incompressive stress to the channel region Ch as a function of thegermanium (Ge) concentration in the mixed crystal layers 8, between thecase in which the damascene gate process is employed and the case inwhich it is not employed.

This graph indicates that using the damascene gate process reduces thegermanium concentration necessary to ensure the same compressive stressand thus decreases the germanium concentration in the mixed crystallayers 8 to thereby allow ensured prevention of crystal defects.

WORKING EXAMPLES

Specific working examples of the embodiment of the present invention andthe results of evaluation on the working examples will be describedbelow.

Working Example 1

A PMOS transistor was fabricated by the same method as that of theabove-described embodiment. As the gate insulating film 14, a siliconoxynitride film was used that was formed by oxidizing the surface of thesilicon substrate 1 exposed at the bottom of the recess 13 by thermaloxidation and then performing nitridation treatment. For the gateelectrode 15, poly-silicon (Poly-Si) was used.

Working Example 2

A PMOS transistor was fabricated by the same method as that of theabove-described embodiment. However, as the gate insulating film 14, ahafnium oxide (HfO₂) film provided to cover the inner wall of the recess13 was used. For the gate electrode 15, titanium nitride was used.

Comparative Example 1

As Comparative example 1 for Working examples 1 and 2, a PMOS transistorwas fabricated by the same method as that for the first working example,except that the mixed crystal layers 8 were not formed.

<Evaluation Result 1>

The off-current and the on-current were measured about the PMOStransistors of Working examples 1 and 2 and Comparative example 1. FIG.7 is a graph showing the result of plotting of the relationships betweenthe off-current and the on-current.

This graph indicates that the on/off ratio of the PMOS transistors ofWorking examples 1 and 2, to which the present invention is applied, isgreatly higher than that of the PMOS of Comparative example 1.

Furthermore, it is confirmed that the on/off ratio is further increasedby using a high dielectric (High-k) film as the gate insulating film 14and employing a metal gate as the gate electrode 15 like in Workingexample 2.

<Evaluation Result 2>

FIG. 8 is a graph showing the results of measurement of theon-resistance value about the PMOS transistors of Working examples 1 and2 and Comparative example 1.

This graph proves that the on-resistance value of the PMOS transistorsof Working examples 1 and 2, to which the present invention is applied,is greatly lower than that of the PMOS of Comparative example 1.

Second Embodiment

Next, as one example of a method for manufacturing a semiconductordevice according to the embodiment of the present invention, a methodfor manufacturing a PMOS transistor in a CMOS transistor will bedescribed below by using the sectional views of FIGS. 9 to 12, whichshow manufacturing steps.

Referring to (a) of FIG. 9, element isolation regions (not shown) areformed on the surface side of a silicon (Si) substrate 1 by using STI(Shallow Trench Isolation) or another method.

Subsequently, on the surface of the silicon substrate 1, a silicondioxide (SiO₂) film is deposited by e.g. oxidation as an anti-channelingprotective film used for ion implantation of an impurity into thesilicon substrate 1.

Subsequently, by an ion implantation method, impurities are introducedinto each of the NMOS transistor region and the PMOS transistor regionin order to carry out element isolation and threshold value adjustment.

Subsequently, the above-described silicon dioxide film is removed toexpose the surface of the silicon substrate 1, and then a gateinsulating film 17 having e.g. a high dielectric (High-k) insulatingfilm is formed. This gate insulating film 17 is formed with a filmthickness of e.g. about 1 nm to 3 nm by a film deposition method such aschemical vapor deposition (CVD) or atomic layer deposition (ALD).

The above-described high dielectric insulating film is formed by using amaterial having a dielectric constant higher than that of silicondioxide. For example, it is formed by using a metal oxide, a metalsilicate, a metal oxynitride, or a nitrided metal silicate of one kindof metal selected from hafnium (Hf), lanthanum (La), aluminum (Al),zirconium (Zn), and tantalum (Ta). As one example of the material, anyof the following materials can be used: metal oxides such as hafniumoxide (HfO₂), aluminum oxide (Al₂O₃), and lanthanum oxide (La₂O₃); metaloxynitrides such as hafnium oxynitride (HfON) and aluminum oxynitride(AlON); metal silicates such as hafnium silicate (HfSiO); and nitridedmetal silicates such as nitrided hafnium silicate (HfSiON).

Furthermore, as one example, the above-described gate insulating film 14may be a component obtained by stacking the above-described highdielectric insulating film on a silicon-based insulating film such as asilicon dioxide film or a silicon nitride film.

Subsequently, a dummy gate electrode film (not shown) composed ofPoly-Si is deposited by e.g. a CVD method to a thickness of about 100 nmto 200 nm. Next, by e.g. a CVD method, a SiN film that will serve as ahard mask is deposited on the dummy gate electrode film to a thicknessof about 30 nm to 100 nm. Subsequently, resist is applied on theabove-described SiN film, and then this resist is patterned by opticallithography (KrF, ArF, F₂) or electron beam (EB) lithography, to therebyform a resist pattern having a gate electrode pattern.

Subsequently, a hard mask 4 is formed by processing the above-describedsilicon nitride film through dry etching in which this resist pattern isused as the mask. At this time, the hard mask 4 is often subjected tothinning and trimming so as to have a line width smaller than that ofthe resist pattern so that a small gate electrode pattern can beobtained.

Thereafter, the resist pattern is removed, and then dry etching for thedummy gate electrode film is performed by using the hard mask 4 as themask, to thereby form a dummy gate electrode 3 composed of Poly-Si.

The etching of the dummy gate electrode film is performed in such a waythat the selection ratio with respect to the high dielectric (High-k)insulating film is ensured, to thereby prevent the silicon substrate 1from being etched.

Thereafter, the above-described resist pattern is removed. By this posttreatment, the gate insulating film 17 covering the surface of thesilicon substrate 1 except for under the dummy gate electrode 3 isremoved, so that the gate insulating film 17 is left only under thedummy gate electrode 3. The line width of the dummy gate electrode 3 atthis time is several nanometers to several tens of nanometers at least.

It is to be noted that, although it is described that the dummy gateelectrode 3 is formed by using Poly-Si in the present example, amorphoussilicon may be used as the material of the dummy gate electrode 3.Furthermore, for the hard mask 4, an insulating film other than theabove-described SiN film may be used.

Referring next to (b) of FIG. 9, offset spacers 5 composed of e.g.silicon nitride (SiN) are formed to a thickness of 1 nm to 10 nm on thesidewalls of the dummy gate insulating film 17, the dummy gate electrode3, and the hard mask 4.

Subsequently, as shown in (c) of FIG. 9, dummy sidewalls 6 composed ofe.g. silicon dioxide (SiO₂) are formed on both the sides of the dummygate insulating film 17, the dummy gate electrode 3, and the hard mask4, for which the offset spacers 5 have been provided.

Here, the dummy sidewalls 6 will be removed by etching selectively withrespect to the offset spacers 5 in a later step. Therefore, it ispreferable that the dummy sidewalls 6 be formed by using a materialwhich can take etching selection ratio with respect to the material ofthe offset spacers 5.

Referring next to (d) of FIG. 9, recess etching for partially removingthe silicon substrate 1 is performed by using the hard mask 4 on thedummy gate electrode 3 and the dummy sidewalls 6 and the like as theetching mask, to thereby form recess regions 7 with a depth of about 50nm to 100 nm.

Through this recess etching, only the recess regions 7 for one of anNMOS transistor and PMOS transistor are formed in some cases, and therecess regions 7 are sequentially formed for both an NMOS transistor andPMOS transistor in other cases.

At this time, resist patterning is carried out on the NMOS transistorside at the time of the formation of the mixed crystal layer for thePMOS transistor, such as silicon germanium (SiGe), and resist patterningis carried out on the PMOS transistor side at the time of the formationof the mixed crystal layer for the NMOS transistor, such as siliconcarbide (SiC), and the protective film of silicon dioxide (SiO₂) usedfor the above-described anti-channeling is left.

It is to be noted that, although it is described that the recess etchingis performed in the state in which the dummy sidewalls 6 have beenprovided in the present example, the present invention can be appliedalso to an example in which the recess etching is performed without theprovision of the dummy sidewalls 6.

Referring next to (e) of FIG. 10, on the surfaces of the recess regions7, i.e., on the surface of the partially etched part of the siliconsubstrate 1, mixed crystal layers 8 composed of silicon (Si) and atomshaving a lattice constant different from that of silicon (Si) areepitaxially grown. At this time, in the PMOS transistor side, a silicongermanium (hereinafter referred to as SiGe) layer composed of silicon(Si) and germanium (Ge) having a lattice constant larger than that ofsilicon (Si) is epitaxially grown as the mixed crystal layers 8.

This SiGe layer will function as source/drain regions throughintroduction of an impurity therein. Simultaneously with the epitaxialgrowth of the SiGe layer, a p-type impurity such as boron (B) isintroduced with a concentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³. Theepitaxial growth is performed in such a way that the germanium (Ge)concentration at this time is in the range of 15 at % to 20 at %. Here,if the germanium (Ge) concentration is increased excessively, adverseeffects due to defects occur as described above. Therefore, a problemthat the concentration cannot be increased exists.

Thereby, the region in the silicon substrate 1 between the mixed crystallayers 8 and directly beneath the dummy gate electrode 3 will functionas a channel region, and as described above by using FIG. 23 about arelated art, compressive stress (arrowheads A) is applied to the channelregion from the mixed crystal layers 8. Thus, escaping force (arrowheadsC) works along the direction of the normal of the silicon substrate 1toward the outside of the silicon substrate 1. However, this escapingforce is suppressed by counteraction (arrowheads D) from the dummy gateelectrode 3, which results in the state in which the application of thecompressive stress is suppressed.

On the other hand, in an NMOS transistor side, a silicon carbide (SiC)layer composed of silicon (Si) and carbon (C) having a lattice constantsmaller than that of silicon (Si) is epitaxially grown as the mixedcrystal layers 8, although not shown in the drawings. Simultaneouslywith the epitaxial growth of the silicon carbide layer, an n-typeimpurity such as arsenic (As) or phosphorous (P) is introduced with aconcentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³. The C concentration in theSiC layer of the mixed crystal layers 8 is set to a value in aconcentration range of 0.5 atm % to 1.5 atm %, in order to preventcrystal defects due to the existence of a high concentration of carbonin the silicon carbide layer and effectively apply stress to the channelregion. This concentration is set to concentration lower than thegermanium (Ge) concentration that has been reported to be the optimumgenerally. This is a merit attributed to the stress enhancement effectdue to the damascene gate structure, which will be described later.

Here, for effective stress application to the channel region, it ispreferable that the mixed crystal layers 8 be so formed as to protrudefrom the surface of the silicon substrate 1. Furthermore, the Geconcentration in the SiGe layer of the mixed crystal layers 8 is set toa value in a concentration range of 15 atm % to 20 atm %, in order toprevent crystal defects due to the existence of a high concentration ofGe in the SiGe layer and effectively apply stress to the channel region.

It is to be noted that, also in the NMOS transistor side, as describedabove by using FIG. 24 about the related art, escaping force issuppressed by counteraction from the dummy gate electrode 3, whichresults in the state in which the application of the tensile stress issuppressed.

It is to be noted that, although it is described that the mixed crystallayers 8 are epitaxially grown simultaneously with impurity introductionin the present example, an impurity may be introduced by ionimplantation in a step subsequent to the epitaxial growth of the mixedcrystal layers 8 performed without impurity introduction.

The epitaxial growth of the mixed crystal layers 8 for the respectiveelement regions is performed in such a way that the NMOS transistorregion is covered by a protective film such as resist in formation ofthe mixed crystal layers 8 for the PMOS transistor region, and isperformed in such a way that the PMOS transistor region is covered by aprotective film such as resist in formation of the mixed crystal layers8 for the NMOS transistor region.

Referring next to (f) of FIG. 10, the dummy sidewalls 6 (seeabove-described (e) of FIG. 10) are removed by e.g. wet etching tothereby expose the surfaces of the offset spacers 5 and the siliconsubstrate 1.

Subsequently, as shown in (g) of FIG. 10, a p-type impurity such asboron ions (B⁺) or indium ions (In⁺) is introduced into the PMOStransistor side by e.g. ion implantation, to thereby formshallow-junction extension regions 9 on the surface side of the siliconsubstrate 1 on both the sides of the offset spacers 5.

At this time, as the condition of the ion implantation, the implantationis performed with implantation energy of 100 eV to 300 eV and a dosageof 5×10¹⁴/cm² to 2×10¹⁵/cm², so that a shallow junction is formed.

On the other hand, although not shown in the drawing, arsenic ions (As⁺)or phosphorous ions (P⁺) are implanted also into the NMOS transistorside e.g. with implantation energy of 100 eV to 300 eV and a dosage of5×10¹⁴/cm² to 2×10¹⁵/cm², so that a shallow junction is formed.

It is to be noted that the ion implantation into the respective elementregions is performed in such a way that the NMOS transistor region iscovered by a protective film such as resist in ion implantation into thePMOS transistor region, and is performed in such a way that the PMOStransistor region is covered by a protective film such as resist in ionimplantation into the NMOS transistor region.

Thereafter, as shown in (h) of FIG. 10, sidewalls 10 composed of e.g.silicon nitride are formed on both the sides of the offset spacers 5.

Subsequently, by ion implantation, an impurity is introduced into thesurfaces of the mixed crystal layers 8 by using the hard mask 4 and thesidewalls 10 as the mask. The purpose of this ion implantation is toreduce the contact resistance of a silicide layer that will be formed onthe surfaces of the mixed crystal layers 8 in a later step.

Subsequently, a refractory metal film (not shown) is formed by e.g.sputtering across the entire surface of the silicon substrate 1,including on the mixed crystal layers 8, in such a manner as to coverthe dummy gate electrode 3, for which the hard mask 4 and the sidewalls10 have been provided. As the refractory metal, cobalt (Co), nickel(Ni), platinum (Pt), or a compound of these metals is used.

Subsequently, the silicon substrate 1 is heated to thereby turn thesurface side of the mixed crystal layers 8 into a silicide, so thatsilicide layers 11 are formed.

Thereafter, the unreacted refractory metal film remaining on the elementisolation regions (not shown) and the sidewalls 10 is selectivelyremoved.

Subsequently, as shown in (i) of FIG. 11, an interlayer insulating film12 composed of e.g. silicon dioxide (SiO₂) is formed across the entiresurface of the silicon substrate 1, including on the silicide layers 11,in such a manner as to cover the dummy gate electrode 3, for which thehard mask 4 and the sidewalls 10 have been provided.

At this time, in some cases, a liner silicon nitride (SiN) film forcontact etching stop is formed and silicon dioxide (SiO₂) or the like isdeposited thereon in a stacked manner to thereby form theabove-described interlayer insulating film 12.

Thereafter, as shown in (j) of FIG. 11, upper part of the interlayerinsulating film 12 and the hard mask 4 are removed by a CMP method untilthe surface of the dummy gate electrode 3 is exposed. The drawing showsthe state before the removal.

Subsequently, as shown in (k) of FIG. 11, the dummy gate electrode 3(see above-described (j) of FIG. 11) is selectively removed by dryetching, to thereby form a recess 13. At this time, the gate insulatingfilm 17 having the high dielectric insulating film is left at the bottomof the recess 13.

For example, in the above-described dry etching, a mixture gas ofhydrogen bromide (HBr) and oxygen (O₂) is used as the etching gas, tothereby selectively etch-remove the dummy gate electrode 3 with respectto the gate insulating film 17.

Thereby, it is avoided in the PMOS transistor that the stress(arrowheads A) applied from the mixed crystal layers 8 to the channelregion Ch directly beneath the dummy gate electrode 3 is suppressed bycounteraction from the dummy gate electrode 3. Thus, the compressivestress to the channel region Ch is increased. Also in the NMOStransistor, the tensile stress to the channel region is increasedsimilarly.

Subsequently, heat treatment is performed for the silicon substrate 1,from which the dummy gate electrode 3 has been removed, at a temperatureof 500° C. to 700° C. for ten seconds to several minutes.

This further increases the stress to the channel region Ch by the mixedcrystal layer 8. Furthermore, this heat treatment can also offer theeffect to recover the damage to the high dielectric (High-k) insulatingfilm.

In the above-described heat treatment, the effect to reduce the leakageis small with a temperature lower than 500° C. In contrast, atemperature higher than 700° C. causes crystallization and thus makes itdifficult to achieve the reliability. Therefore, the treatmenttemperature is set to the above-described temperature.

Referring next to (1) of FIG. 12, by e.g. a chemical vapor deposition(CVD) method, an atomic layer deposition (ALD) method, a physical vapordeposition (PVD) method or a plating method, a gate electrode film 15′composed of e.g. titanium nitride (TiN) is so formed on the gateinsulating film 17 as to fill the recess 13, in which the gateinsulating film 17 has been provided. As the material of the gateelectrode film 15′, a metal such as titanium (Ti), ruthenium (Ru),hafnium (Hf), iridium (Ir), tungsten (W), molybdenum (Mo), lanthanum(La), nickel (Ni), copper (Cu), or aluminum (Al), or a metal compoundsuch as a silicon compound or nitrogen (N) compound of any of thesemetals is used. This can prevent the depletion of the gate electrodecompared with the case of employing a gate electrode composed ofpoly-silicon (Poly-Si).

However, the present invention can be applied also to the case ofemploying poly-silicon for the gate electrode film 15′.

Here, in the deposition of the above-described gate insulating film 17and the gate electrode film 15′, the deposition condition is socontrolled that the state in which the stress is applied from the mixedcrystal layers 8 to the channel region Ch can be kept. Specifically, thepressure, power, gas flow rate, or temperature in the film deposition iscontrolled.

Referring next to (m) of FIG. 12, the above-described gate electrodefilm 15′ (see above-described (1) of FIG. 12) removed by e.g. a chemicalmechanical polishing (CMP) method until the surface of the interlayerinsulating film 12 is exposed, to thereby form a gate electrode 15 onthe gate insulating film 17 in the recess 13.

Through the above-described steps, a CMOSFET is formed.

Thereafter, as shown in (n) of FIG. 12, an interlayer insulating film 16is further formed on the interlayer insulating film 12, including on thegate electrode 15, and contacts and metal interconnects are formed, sothat the semiconductor device is fabricated.

According to such a method for manufacturing a semiconductor device anda semiconductor device obtained by this method, the recess 13 is formedby removing the dummy gate electrode 3. Thus, it is avoided that stressapplied from the mixed crystal layers 8 to the channel region Chdirectly beneath the dummy gate electrode 3 is suppressed bycounteraction from the above-described dummy gate electrode 3.Thereafter, the gate electrode 15 is so formed on the gate insulatingfilm 14 in the recess 13 that the stress state is kept. This allowseffective stress application to the channel region Ch, and hence canstrain the channel region Ch to thereby enhance the carrier mobility.

In addition, this effective stress application to the channel region Chmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layers 8. This feature can surely prevent crystal defectsattributed to the existence of a high concentration of theabove-described atoms in the mixed crystal layers 8.

Furthermore, if the gate insulating film 17 having the high dielectricinsulating film is formed on the sidewall of the gate electrode, theparasitic capacitance between the sidewall of the gate electrode and themixed crystal layers 8 to serve as the source and drain becomes higher.On the other hand, in the present second embodiment, the gate insulatingfilm 17 is not formed on the sidewall of the gate electrode 15.Therefore, the parasitic capacitance between the sidewall of the gateelectrode 15 and the mixed crystal layers 8 to serve as the source anddrain becomes lower with respect to the fringe capacitance of the gateelectrode 15. This can enhance the operating speed of the MOS transistorcompared with the case in which the gate insulating film 17 is formed onthe sidewall of the gate electrode 15.

Consequently, characteristics of the transistor can be enhanced.

Third Embodiment

Next, as one example of a method for manufacturing a semiconductordevice according to the embodiment of the present invention, a methodfor manufacturing a PMOS transistor in a CMOS transistor will bedescribed below by using the sectional views of FIGS. 13 to 16, whichshow manufacturing steps.

Referring to (a) of FIG. 13, element isolation regions (not shown) areformed on the surface side of a silicon (Si) substrate 1 by using STI(Shallow Trench Isolation) or another method.

Subsequently, on the surface of the Si substrate 1, a silicon dioxide(SiO₂) film is deposited by e.g. oxidation as an anti-channelingprotective film used for ion implantation of an impurity into thesilicon substrate 1. Subsequently, by an ion implantation method,impurities are introduced into each of the NMOS transistor region andthe PMOS transistor region in order to carry out element isolation andthreshold value adjustment.

Subsequently, the above-described silicon dioxide film is removed toexpose the surface of the silicon substrate 1, and then a gateinsulating film 17 having e.g. a high dielectric (High-k) insulatingfilm is formed. This gate insulating film 17 is formed with a filmthickness of e.g. about 1 nm to 3 nm by a film deposition method such aschemical vapor deposition (CVD) or atomic layer deposition (ALD).

The above-described high dielectric insulating film is formed by using amaterial having a dielectric constant higher than that of silicondioxide. For example, it is formed by using a metal oxide, a metalsilicate, a metal oxynitride, or a nitrided metal silicate of one kindof metal selected from hafnium (Hf), lanthanum (La), aluminum (Al),zirconium (Zn), and tantalum (Ta). As one example of the material, anyof the following materials can be used: metal oxides such as hafniumoxide (HfO₂), aluminum oxide (Al₂O₃), and lanthanum oxide (La₂O₃); metaloxynitrides such as hafnium oxynitride (HfON) and aluminum oxynitride(AlON); metal silicates such as hafnium silicate (HfSiO); and nitridedmetal silicates such as nitrided hafnium silicate (HfSiON).

Furthermore, as one example, the above-described gate insulating film 17may be a component obtained by stacking the above-described highdielectric insulating film on a silicon-based insulating film such as asilicon dioxide film or a silicon nitride film.

Subsequently, a cap film 18 is formed on the gate insulating film 17.This cap film 18 will serve as an etching stopper for preventing etchingdamage from entering the underlying gate insulating film 17 when a dummygate formed on the cap film 18 is removed in a later step. The cap film18 is formed of e.g. a titanium nitride (TiN) film. This cap film 18 isformed with a film thickness of e.g. about 3 nm to 10 nm by a filmdeposition method such as chemical vapor deposition (CVD) or atomiclayer deposition (ALD).

Subsequently, a dummy gate electrode film 41 composed of Poly-Si isdeposited by e.g. a CVD method to a thickness of about 100 nm to 200 nm.

Next, by e.g. the CVD method, a silicon nitride film that will serve asa hard mask formation film 42 is deposited on the dummy gate electrodefilm to a thickness of about 30 nm to 100 nm. Subsequently, resist isapplied on the above-described SiN film, and then this resist ispatterned by optical lithography (KrF, ArF, F₂) or electron beam (EB)lithography, to thereby form a resist pattern having a gate electrodepattern.

Subsequently, a hard mask 4 is formed by processing the above-describedhard mask formation film 42 through dry etching in which this resistpattern is used as the mask. At this time, the hard mask 4 is oftensubjected to thinning and trimming so as to have a line width smallerthan that of the resist pattern so that a small gate electrode patterncan be obtained.

Thereafter, the above-described resist pattern is removed, and then dryetching for the dummy gate electrode film 41 is performed by using thehard mask 4 as the etching mask, to thereby form a dummy gate electrode3 composed of Poly-Si.

The etching of the dummy gate electrode film is performed in such a waythat the selection ratio with respect to the cap film 18 or the gateinsulating film 17 of the high dielectric (High-k) insulating film isensured, to thereby prevent the silicon substrate 1 from being etched.

Thereafter, the above-described resist pattern is removed. By this posttreatment, the gate insulating film 17 covering the surface of thesilicon substrate 1 except for under the dummy gate electrode 3 isremoved, so that the gate insulating film 17 is left only under thedummy gate electrode 3. The line width of the dummy gate electrode 3 atthis time is several nanometers to several tens of nanometers at least.

It is to be noted that, although it is described that the dummy gateelectrode 3 is formed by using Poly-Si in the present example, amorphoussilicon may be used as the material of the dummy gate electrode 3.Furthermore, for the hard mask 4, an insulating film other than theabove-described SiN may be used.

Referring next to (c) of FIG. 13, offset spacers 5 composed of e.g.silicon nitride (SiN) are formed to a thickness of 1 nm to 10 nm on thesidewalls of the gate insulating film 17, the cap film 18, the dummygate electrode 3, and the hard mask 4.

Subsequently, dummy sidewalls 6 composed of e.g. silicon dioxide (SiO₂)are formed on both the sides of the gate insulating film 17, the capfilm 18, the dummy gate electrode 3, and the hard mask 4 through theabove-described offset spacer 5, for which the offset spacers 5 havebeen provided.

Here, the dummy sidewalls 6 will be removed by etching selectively withrespect to the offset spacers 5 in a later step. Therefore, it ispreferable that the dummy sidewalls 6 be formed by using a materialwhich can take etching selection ratio with respect to the material ofthe offset spacers 5.

Referring next to (d) of FIG. 13, recess etching for partially removingthe silicon substrate 1 is performed by using the hard mask 4 on thedummy gate electrode 3 and the dummy sidewalls 6 as the mask, to therebyform recess regions 7 with a depth of about 50 nm to 100 nm.

Through this recess etching, only the recess regions 7 for one of anNMOS and PMOS are formed in some cases, and the recess regions 7 aresequentially formed for both an NMOS and PMOS in other cases.

At this time, resist patterning is carried out on the NMOS transistorside at the time of the formation of the mixed crystal layer for thePMOS transistor, such as silicon germanium (SiGe), and resist patterningis carried out on the PMOS transistor side at the time of the formationof the mixed crystal layer for the NMOS transistor, such as siliconcarbide (SiC), and the protective film of silicon dioxide (SiO₂) usedfor the above-described anti-channeling is left.

It is to be noted that, although it is described that the recess etchingis performed in the state in which the dummy sidewalls 6 have beenprovided in the present example, the present invention can be appliedalso to an example in which the recess etching is performed without theprovision of the dummy sidewalls 6.

Referring next to (e) of FIG. 14, on the surfaces of the recess regions7, i.e., on the surface of the partially etched part of the siliconsubstrate 1, mixed crystal layers 8 composed of silicon (Si) and atomshaving a lattice constant different from that of silicon (Si) areepitaxially grown. At this time, in the PMOS transistor side, a silicongermanium (hereinafter referred to as SiGe) layer composed of silicon(Si) and germanium (Ge) having a lattice constant larger than that ofsilicon (Si) is epitaxially grown as the mixed crystal layers 8.

This SiGe layer will function as source/drain regions throughintroduction of an impurity therein. Simultaneously with the epitaxialgrowth of the SiGe layer, a p-type impurity such as boron (B) isintroduced with a concentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³. Theepitaxial growth is performed in such a way that the germanium (Ge)concentration at this time is in the range of 15 at % to 20 at %. If thegermanium (Ge) concentration is increased excessively, adverse effectsdue to defects occur as described above. Therefore, a problem that theconcentration cannot be increased exists.

Therefore, the region in the silicon substrate 1 between the mixedcrystal layers 8 and directly beneath the dummy gate electrode 3 willfunction as a channel region, and as described above by using FIG. 23about a related art, compressive stress (arrowheads A) is applied to thechannel region from the mixed crystal layers 8. Thus, escaping force(arrowheads C) works along the direction of the normal of the Sisubstrate 1 toward the outside of the silicon substrate 1. However, thisescaping force is suppressed by counteraction (arrowheads D) from thedummy gate electrode 3, which results in the state in which theapplication of the compressive stress is suppressed.

On the other hand, in an NMOS transistor side, a silicon carbide (SiC)layer composed of silicon (Si) and carbon (C) having a lattice constantsmaller than that of silicon (Si) is epitaxially grown as the mixedcrystal layers 8, although not shown in the drawings. Simultaneouslywith the epitaxial growth of the silicon carbide layer, an n-typeimpurity such as arsenic (As) or phosphorous (P) is introduced with aconcentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³. The C concentration in theSiC layer of the mixed crystal layers 8 is set to a value in aconcentration range of 0.5 atm % to 1.5 atm %, in order to preventcrystal defects due to the existence of a high concentration of C in thesilicon carbide layer and effectively apply stress to the channelregion. This concentration is set to concentration lower than thegermanium (Ge) concentration that has been reported to be the optimumgenerally. This is a merit attributed to the stress enhancement effectdue to the damascene gate structure, which will be described later.

Here, for effective stress application to the channel region, it ispreferable that the mixed crystal layers 8 be so formed as to protrudefrom the surface of the silicon substrate 1. Furthermore, the Geconcentration in the SiGe layer of the mixed crystal layers 8 is set toa value in a concentration range of 15 atm % to 20 atm %, in order toprevent crystal defects due to the existence of a high concentration ofGe in the SiGe layer and effectively apply stress to the channel region.

It is to be noted that, also in the NMOS transistor side, as describedabove by using FIG. 24 about the related art, escaping force issuppressed by counteraction from the dummy gate electrode 3, whichresults in the state in which the application of the tensile stress issuppressed.

It is to be noted that, although it is described that the mixed crystallayers 8 are epitaxially grown simultaneously with impurity introductionin the present example, an impurity may be introduced by ionimplantation in a step subsequent to the epitaxial growth of the mixedcrystal layers 8 performed without impurity introduction.

The epitaxial growth of the mixed crystal layers 8 for the respectiveelement regions is performed in such a way that the NMOS transistorregion is covered by a protective film such as resist in formation ofthe mixed crystal layers 8 for the PMOS transistor region, and isperformed in such a way that the PMOS transistor region is covered by aprotective film such as resist in formation of the mixed crystal layers8 for the NMOS transistor region.

Referring next to (f) of FIG. 14, the dummy sidewalls 6 (seeabove-described (e) of FIG. 14) are removed by e.g. wet etching tothereby expose the surfaces of the offset spacers 5 and the siliconsubstrate 1.

Subsequently, as shown in (g) of FIG. 14, a p-type impurity such asboron ions (B⁺) or indium ions (In⁺) is introduced into the PMOStransistor side by e.g. ion implantation, to thereby formshallow-junction extension regions 9 on the surface side of the siliconsubstrate 1 on both the sides of the offset spacers 5.

At this time, as the condition of the ion implantation, the implantationis performed with implantation energy of 100 eV to 300 eV and a dosageof 5×10¹⁴/cm² to 2×10¹⁵/cm², so that a shallow junction is formed.

On the other hand, arsenic ions (As⁺) or phosphorous ions (P⁺) areimplanted also into the NMOS transistor side e.g. with implantationenergy of 100 eV to 300 eV and a dosage of 5×10¹⁴/cm² to 2×10¹⁵/cm², sothat a shallow junction is formed.

The ion implantation into the respective element regions is performed insuch a way that the NMOS transistor region is covered by a protectivefilm such as resist in ion implantation into the PMOS transistor region,and is performed in such a way that the PMOS transistor region iscovered by a protective film such as resist in ion implantation into theNMOS transistor region.

Thereafter, as shown in (h) of FIG. 14, sidewalls 10 composed of e.g.silicon nitride are formed again on both the sides of the dummy gateelectrode 3 with the intermediary of the offset spacers 5.

Subsequently, by ion implantation, an impurity is introduced into thesurfaces of the mixed crystal layers 8 by using the hard mask 4 and thesidewalls 10 as the mask. The purpose of this ion implantation is toreduce the contact resistance of a silicide layer that will be formed onthe surfaces of the mixed crystal layers 8 in a later step.

Subsequently, a refractory metal film (not shown) is formed by e.g.sputtering across the entire surface of the silicon substrate 1,including on the mixed crystal layers 8, in such a manner as to coverthe dummy gate electrode 3, for which the hard mask 4 and the sidewalls10 have been provided. As the refractory metal, cobalt (Co), nickel(Ni), platinum (Pt), or a compound of these metals is used.

Subsequently, the silicon substrate 1 is heated to thereby turn thesurface side of the mixed crystal layers 8 into a silicide, so thatsilicide layers 11 are formed.

Thereafter, the unreacted refractory metal film remaining on the elementisolation regions (not shown) and the sidewalls 10 is selectivelyremoved.

Subsequently, as shown in (i) of FIG. 15, an interlayer insulating film12 composed of e.g. silicon dioxide (SiO₂) is formed across the entiresurface of the silicon substrate 1, including on the silicide layers 11,in such a manner as to cover the dummy gate electrode 3, for which thehard mask 4 and the sidewalls 10 have been provided.

At this time, in some cases, a liner silicon nitride (SiN) film forcontact etching stop is formed and silicon dioxide (SiO₂) or the like isdeposited thereon in a stacked manner to thereby form theabove-described interlayer insulating film 12.

Thereafter, as shown in (j) of FIG. 15, upper part of the interlayerinsulating film 12 and the hard mask 4 (see above-described (i) of FIG.15) are removed by a CMP method until the surface of the dummy gateelectrode 3 is exposed. The drawing shows the state before the removal.

Subsequently, as shown in (k) of FIG. 15, the dummy gate electrode 3(see above-described (j) of FIG. 15) is selectively removed by dryetching, to thereby form a recess 13. At this time, the cap film 18 atthe bottom of the recess 13 serves as the etching stopper, and thusetching damage does not enter the gate insulating film 17.

For example, in the above-described dry etching, a mixture gas ofhydrogen bromide (HBr) and oxygen (O₂) is used as the etching gas.

Moreover, as shown in (1) of FIG. 15, the cap film 18 (seeabove-described (k) of FIG. 15) is selectively removed by wet etching ordry etching that gives little etching damage to the underlying layer, tothereby leave the gate insulating film 17 at the bottom of the recess13.

For example, if the cap film 18 is formed of titanium nitride andremoved by wet etching, an ammonia hydrogen peroxide mixture solution isused as the etchant.

The above-described cap film 18 is often used as it is as a metal forwork function control for the metal gate, and is often left withoutbeing removed. Furthermore, in e.g. the case of fabricating the workfunction control metals of the NMOS transistor and the PMOS transistordifferently like the dual metal gates, the cap film 18 may be left foronly either transistor.

Thereby, it is avoided in the PMOS transistor that the stress appliedfrom the mixed crystal layers 8 to the channel region Ch directlybeneath the dummy gate electrode 3 is suppressed by counteraction fromthe dummy gate electrode 3. Thus, the compressive stress to the channelregion Ch is increased. Also in the NMOS transistor, the tensile stressto the channel region is increased similarly.

Subsequently, heat treatment is performed for the silicon substrate 1,from which the dummy gate electrode 3 has been removed, at a temperatureof 500° C. to 700° C. for ten seconds to several minutes.

This further increases the stress to the channel region Ch by the mixedcrystal layer 8. Furthermore, this heat treatment can also offer theeffect to recover the damage to the high dielectric (High-k) insulatingfilm.

In the above-described heat treatment, the effect to reduce the leakageis small with a temperature lower than 500° C. In contrast, atemperature higher than 700° C. causes crystallization and thus makes itdifficult to achieve the reliability. Therefore, the treatmenttemperature is set to the above-described temperature.

Referring next to (m) of FIG. 16, by e.g. a chemical vapor deposition(CVD) method, an atomic layer deposition (ALD) method, a physical vapordeposition (PVD) method or a plating method, a gate electrode film 15′composed of e.g. titanium nitride (TiN) is so formed on the gateinsulating film 17 as to fill the recess 13, in which the gateinsulating film 17 has been provided. As the material of the gateelectrode film 15′, a metal such as titanium (Ti), ruthenium (Ru),hafnium (Hf), iridium (Ir), tungsten (W), molybdenum (Mo), lanthanum(La), nickel (Ni), copper (Cu), or aluminum (Al), or a metal compoundsuch as a silicon compound or nitrogen (N) compound of any of thesemetals is used. This can prevent the depletion of the gate electrodecompared with the case of employing a gate electrode composed ofpoly-silicon (Poly-Si).

However, the present invention can be applied also to the case ofemploying poly-silicon for the gate electrode film 15′.

In the deposition of the above-described gate insulating film 17 and thegate electrode film 15′, the deposition condition is so controlled thatthe state in which the stress is applied from the mixed crystal layers 8to the channel region Ch can be kept. Specifically, the pressure, power,gas flow rate, or temperature in the film deposition is controlled.

Referring next to (n) of FIG. 16, the above-described gate electrodefilm 15′ (see above-described (m) of FIG. 16) is removed by e.g. achemical mechanical polishing (CMP) method until the surface of theinterlayer insulating film 12 is exposed, to thereby form a gateelectrode 15 on the gate insulating film 17 in the recess 13.

Through the above-described steps, a CMOSFET is formed.

Thereafter, as shown in (o) of FIG. 16, an interlayer insulating film 16is further formed on the interlayer insulating film 12, including on thegate electrode 15, and contacts and metal interconnects are formed, sothat the semiconductor device is fabricated, although not shown in thedrawings.

According to such a method for manufacturing a semiconductor device anda semiconductor device obtained by this method, the recess 13 is formedby removing the dummy gate electrode 3. Thus, it is avoided that stressapplied from the mixed crystal layers 8 to the channel region Chdirectly beneath the dummy gate electrode 3 is suppressed bycounteraction from the dummy gate electrode 3. Thereafter, the gateelectrode 15 is so formed on the gate insulating film 14 in the recess13 that the stress state is kept. This allows effective stressapplication to the above-described channel region Ch, and hence canstrain the channel region Ch to thereby enhance the carrier mobility.

In addition, this effective stress application to the channel region Chmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layers 8. This feature can surely prevent crystal defectsattributed to the existence of a high concentration of theabove-described atoms in the mixed crystal layers 8.

Consequently, characteristics of the transistor can be enhanced.

Fourth Embodiment

Next, as one example of a method for manufacturing a semiconductordevice according to the embodiment of the present invention, a methodfor manufacturing an NMOS transistor and a PMOS transistor in a CMOStransistor will be described below by using the sectional views of FIGS.17 to 18, which show manufacturing steps.

The following structure is formed similarly to the steps described withthe drawings from (a) of FIG. 13 to (k) of FIG. 15 in theabove-described third embodiment.

Namely, referring first to (a) of FIG. 17, element isolation regions(not shown) are formed on the surface side of a silicon (Si) substrate 1by using STI (Shallow Trench Isolation) or another method.

Subsequently, by an ion implantation method, impurities are introducedinto each of the NMOS transistor region and the PMOS transistor regionin order to carry out element isolation and threshold value adjustment.

Subsequently, on the surface of the silicon substrate 1, a gateinsulating film 17 having e.g. a high dielectric (High-k) insulatingfilm is formed. This gate insulating film 17 is formed with a filmthickness of e.g. about 1 nm to 3 nm by a film deposition method such aschemical vapor deposition (CVD) or atomic layer deposition (ALD).

The above-described high dielectric insulating film is formed by using amaterial having a dielectric constant higher than that of silicondioxide. For example, it is formed by using a metal oxide, a metalsilicate, a metal oxynitride, or a nitrided metal silicate of one kindof metal selected from hafnium (Hf), lanthanum (La), aluminum (Al),zirconium (Zn), and tantalum (Ta). As one example of the material, anyof the following materials can be used: metal oxides such as hafniumoxide (HfO₂), aluminum oxide (Al₂O₃), and lanthanum oxide (La₂O₃); metaloxynitrides such as hafnium oxynitride (HfON) and aluminum oxynitride(AlON); metal silicates such as hafnium silicate (HfSiO); and nitridedmetal silicates such as nitrided hafnium silicate (HfSiON).

Furthermore, as one example, the above-described gate insulating film 17may be a component obtained by stacking the above-described highdielectric insulating film on a silicon-based insulating film such as asilicon dioxide film or a silicon nitride film.

Subsequently, a cap film 18 is formed on the gate insulating film 17.

This cap film 18 will serve as an etching stopper for preventing etchingdamage from entering the underlying gate insulating film 17 when a dummygate formed on the cap film 18 is removed in a later step. The cap film18 is formed of e.g. a titanium nitride (TiN) film. The above-describedcap film 18 is formed with a film thickness of e.g. about 3 nm to 10 nmby a film deposition method such as chemical vapor deposition (CVD) oratomic layer deposition (ALD).

Subsequently, a dummy gate electrode film (not shown) composed ofPoly-Si is deposited by e.g. a CVD method to a thickness of about 100 nmto 200 nm.

Next, by e.g. the CVD method, a silicon nitride film that will serve asa hard mask is deposited on the dummy gate electrode film to a thicknessof about 30 nm to 100 nm.

Subsequently, a hard mask (not shown) is formed by processing theabove-described silicon nitride film through dry etching in which aresist pattern is used as the mask.

Thereafter, the above-described resist pattern is removed, and then dryetching for the dummy gate electrode film is performed by using the hardmask as the mask, to thereby form a dummy gate electrode (not shown)composed of Poly-Si.

The etching of the dummy gate electrode film is performed in such a waythat the selection ratio with respect to the cap film 18 and the gateinsulating film 17 of the high dielectric (High-k) insulating film isensured, to thereby prevent the silicon substrate 1 from being etched.

Thereafter, the above-described resist pattern is removed. By this posttreatment, the gate insulating film 17 covering the surface of thesilicon substrate 1 except for under the dummy gate electrode isremoved, so that the gate insulating film 17 is left only under thedummy gate electrode. The line width of the dummy gate electrode at thistime is several nanometers to several tens of nanometers at least.

Next, offset spacers 5 composed of e.g. silicon nitride (SiN) are formedto a thickness of 1 nm to 10 nm on the sidewalls of the gate insulatingfilm 17, the cap film 18, the dummy gate electrode 3, and the hard mask4.

Subsequently, dummy sidewalls (not shown) composed of e.g. silicondioxide (SiO₂) are formed on both the sides of the gate insulating film17, the cap film 18, the dummy gate electrode, and the hard mask, forwhich the offset spacers 5 have been provided.

Here, the dummy sidewalls will be removed by etching selectively withrespect to the offset spacers 5 in a later step. Therefore, it ispreferable that the dummy sidewalls be formed by using a material whichcan take etching selection ratio with respect to the material of theoffset spacers 5.

Next, recess etching for partially removing the silicon substrate 1 isperformed by using the hard mask on the dummy gate electrode and thedummy sidewalls as the etching mask, to thereby form recess regions 7with a depth of about 50 nm to 100 nm.

Through this recess etching, only the recess regions 7 for one of anNMOS and PMOS are formed in some cases, and the recess regions 7 aresequentially formed for both an NMOS and PMOS in other cases.

At this time, resist patterning is carried out on the NMOS transistorside at the time of the formation of the mixed crystal layer for thePMOS transistor, such as silicon germanium (SiGe), and resist patterningis carried out on the PMOS transistor side at the time of the formationof the mixed crystal layer for the NMOS transistor, such as siliconcarbide (SiC), and the protective film of silicon dioxide (SiO₂) usedfor the above-described anti-channeling is left.

Next, on the surfaces of the recess regions 7, i.e., on the surface ofthe partially etched part of the silicon substrate 1, mixed crystallayers 8 (8 p) composed of silicon (Si) and atoms having a latticeconstant different from that of silicon (Si) are epitaxially grown.

At this time, in the PMOS transistor side, a silicon germanium(hereinafter referred to as SiGe) layer composed of silicon (Si) andgermanium (Ge) having a lattice constant larger than that of silicon(Si) is epitaxially grown as the mixed crystal layers 8.

Thereby, the region in the silicon substrate 1 between the mixed crystallayers 8 p and directly beneath the dummy gate electrode will functionas a channel region, and compressive stress is applied to the channelregion from the above-described mixed crystal layers 8 p.

On the other hand, in an NMOS transistor side, a silicon carbide (SiC)layer composed of silicon (Si) and carbon (C) having a lattice constantsmaller than that of silicon (Si) is epitaxially grown as the mixedcrystal layers 8 (8 n). Simultaneously with the epitaxial growth of thesilicon carbide layer, an n-type impurity such as arsenic (As) orphosphorous (P) is introduced with a concentration of 1×10¹⁹/cm³ to5×10²⁰/cm³.

The C concentration in the SiC layer of the mixed crystal layers 8 n isset to a value in a concentration range of 0.5 atm % to 1.5 atm %, inorder to prevent crystal defects due to the existence of a highconcentration of carbon (C) in the silicon carbide layer and effectivelyapply stress to the channel region. This concentration is set toconcentration lower than the germanium (Ge) concentration that has beenreported to be the optimum generally. This is a merit attributed to thestress enhancement effect due to the damascene gate structure, whichwill be described later.

Here, for effective stress application to the channel region, it ispreferable that the mixed crystal layers 8 be so formed as to protrudefrom the surface of the silicon substrate 1.

Furthermore, the Ge concentration in the SiGe layer of the mixed crystallayers 8 p is set to a value in a concentration range of 15 atm % to 20atm %, in order to prevent crystal defects due to the existence of ahigh concentration of Ge in the SiGe layer and effectively apply stressto the channel region.

Next, the dummy sidewalls are removed by e.g. wet etching to therebyexpose the surfaces of the offset spacers 5 and the silicon substrate 1.

Subsequently, a p-type impurity such as boron ions (B⁺) or indium ions(In⁺) is introduced into the PMOS transistor side by e.g. ionimplantation, to thereby form shallow-junction extension regions 9 (9 p)on the surface side of the silicon substrate 1 on both the sides of theoffset spacers 5.

At this time, as the condition of the ion implantation, the implantationis performed with implantation energy of 100 eV to 300 eV and a dosageof 5×10¹⁴/cm² to 2×10¹⁵/cm², so that a shallow junction is formed.

On the other hand, arsenic ions (As⁺) or phosphorous ions (P⁺) areimplanted also into the NMOS transistor side e.g. with implantationenergy of 100 eV to 300 eV and a dosage of 5×10¹⁴/cm² to 2×10¹⁵/cm², sothat a shallow junction extension regions 9 (9 n) are formed.

It is to be noted that the ion implantation into the respective elementregions is performed in such a way that the NMOS transistor region iscovered by a protective film such as resist in ion implantation into thePMOS transistor region, and is performed in such a way that the PMOStransistor region is covered by a protective film such as resist in ionimplantation into the NMOS transistor region.

Thereafter, sidewalls 10 composed of e.g. silicon nitride are formed onboth the sides of the offset spacers 5.

Subsequently, by an ion implantation method, impurities in matching withthe conductivity types of the respective mixed crystal layers 8 areintroduced into the surfaces of the respective mixed crystal layers 8with use of the hard mask 4 and the sidewalls 10 as the mask. This ionimplantation is performed in order to reduce the contact resistance of asilicide layer that will be formed on the surfaces of the mixed crystallayers 8 in a later step.

Subsequently, a refractory metal film (not shown) is formed by e.g.sputtering across the entire surface of the silicon substrate 1,including on the mixed crystal layers 8, in such a manner as to coverthe dummy gate electrode 3, for which the hard mask 4 and the sidewalls10 have been provided. As the refractory metal, cobalt (Co), nickel(Ni), platinum (Pt), or a compound of these metals is used.

Subsequently, the silicon substrate 1 is heated to thereby turn thesurface side of the mixed crystal layers 8 into a silicide, so thatsilicide layers 11 are formed.

Thereafter, the unreacted refractory metal film remaining on the elementisolation regions (not shown) and the sidewalls 10 is selectivelyremoved.

Subsequently, an interlayer insulating film 12 composed of e.g. silicondioxide (SiO₂) is formed across the entire surface of the siliconsubstrate 1, including on the silicide layers 11, in such a manner as tocover the dummy gate electrode, for which the hard mask and thesidewalls 10 have been provided.

At this time, in some cases, a liner silicon nitride (SiN) film forcontact etching stop is formed and silicon dioxide (SiO₂) or the like isdeposited thereon in a stacked manner to thereby form theabove-described interlayer insulating film 12.

Thereafter, the interlayer insulating film 12 and the hard mask areremoved by a CMP method until the surface of the dummy gate electrode isexposed.

Subsequently, the dummy gate electrode is selectively removed by dryetching, to thereby form a recess 13. At this time, the cap film 18 atthe bottom of the recess 13 serves as the etching stopper, and thusetching damage does not enter the gate insulating film 17.

For example, in the above-described dry etching, a mixture gas ofhydrogen bromide (HBr) and oxygen (O₂) is used as the etching gas.

Subsequently, as shown in (b) of FIG. 17, a resist mask 31 is so formedas to cover the PMOS transistor side. This resist mask 31 is formed bynormal resist application technique and lithography technique.

Subsequently, the above-described cap film 18 on the above-describedNMOS transistor side (see above-described (a) of FIG. 17) is removed. Inetching of this cap film 18, the cap film 18 is selectively removed bywet etching or dry etching that gives little etching damage to theunderlying gate insulating film 17, to thereby leave the gate insulatingfilm 17 at the bottom of the recess 13 on the above-described NMOStransistor side.

For example, if wet etching is used, an ammonia hydrogen peroxidemixture solution is used as the etchant.

Thereby, it is avoided in the PMOS transistor that the stress appliedfrom the mixed crystal layers 8 to the channel region Ch directlybeneath the dummy gate electrode is suppressed by counteraction from thedummy gate electrode 3. Thus, the compressive stress to the channelregion Ch is increased. Also in the NMOS transistor, the tensile stressto the channel region is increased similarly.

Subsequently, heat treatment is performed for the silicon substrate 1,from which the dummy gate electrode has been removed, at a temperatureof 500° C. to 700° C. for ten seconds to several minutes.

This further increases the stress to the channel region Ch by the mixedcrystal layer 8. Furthermore, this heat treatment can also offer theeffect to recover the damage to the high dielectric (High-k) insulatingfilm.

In the above-described heat treatment, the effect to reduce the leakageis small with a temperature lower than 500° C. In contrast, atemperature higher than 700° C. causes crystallization and thus makes itdifficult to achieve the reliability. Therefore, the treatmenttemperature is set to the above-described temperature.

Subsequently, as shown in (c) of FIG. 18, a work function control film19 that controls a work function is formed on the inner surface of theabove-described recess 13. The above-described work function controlfilm 19 is formed by a chemical vapor deposition (CVD) method or anatomic layer deposition (ALD) method or a physical vapor deposition(PVD) method, and is formed by using e.g. a metal such as tantalum (Ta),hafnium (Hf), lanthanum (La), nickel (Ni), copper (Cu), or aluminum(Al). Alternatively, it is formed by using a silicon compound or anitride of these metals.

Subsequently, a gate electrode film 15′ composed of e.g. a metal isformed in such a state as to fill the recess 13, in which the workfunction control film 19 has been provided, by e.g. a chemical vapordeposition (CVD) method, an atomic layer deposition (ALD) method, aphysical vapor deposition (PVD) method, or a plating method. As thematerial for forming this gate electrode film 15′, a low-resistancemetal such as tungsten (W), copper (Cu), or aluminum (Al) is used.

In the deposition of the above-described work function control film 19and the gate electrode film 15′, the deposition condition is socontrolled that the state in which the stress is applied from the mixedcrystal layers 8 to the channel region Ch can be kept. Specifically, thepressure, power, gas flow rate, or temperature in the film deposition iscontrolled.

Subsequently, as shown in (d) of FIG. 18, the above-described gateelectrode film 15′ (see above-described (m) of FIG. 16) and a part ofthe work function control film 19 are removed by e.g. a chemicalmechanical polishing (CMP) method until the surface of the interlayerinsulating film 12 is exposed. Thereby, in the NMOS transistor, a gateelectrode 15 is formed on the gate insulating film 17 in the recess 13with the intermediary of the work function control film 19. Furthermore,in the PMOS transistor, the gate electrode 15 is formed over the gateinsulating film 17 and the cap film 18 in the recess 13 with theintermediary of the work function control film 19.

Through the above-described steps, a CMOSFET is formed.

Thereafter, an interlayer insulating film is further formed on theinterlayer insulating film 12, including on the gate electrode 15, andcontacts and metal interconnects are formed, so that the semiconductordevice is fabricated, although not shown in the drawings.

It is preferable to form an adhesion layer when the above-described gateelectrode 15 is formed. For example, if tungsten (W) is used as the gateelectrode 15, a titanium nitride (TiN) film is used as the adhesionlayer. If aluminum (Al) is used as the gate electrode 15, a titanium(Ti) film is used as the adhesion layer. If copper is used as the gateelectrode 15, a tantalum (Ta) film is used as the adhesion layer.

According to such a method for manufacturing a semiconductor device anda semiconductor device obtained by this method, the recess 13 is formedby removing the dummy gate electrode. Thus, it is avoided that stressapplied from the mixed crystal layers 8 to the channel region Chdirectly beneath the dummy gate electrode is suppressed by counteractionfrom the dummy gate electrode. Thereafter, the gate electrode 15 is soformed on the gate insulating film 14 in the recess 13 that the stressstate is kept. This allows effective stress application to the channelregion Ch, and hence can strain the channel region Ch to thereby enhancethe carrier mobility.

In addition, this effective stress application to the channel region Chmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layers 8. This feature can surely prevent crystal defectsattributed to the existence of a high concentration of theabove-described atoms in the mixed crystal layers 8.

In addition, by the provision of the work function control film 19, thework functions of the transistors are controlled, which allows furtherenhancement in the carrier mobility.

Consequently, characteristics of the transistor can be enhanced.

Fifth Embodiment

As one example of a method for manufacturing a semiconductor deviceaccording to the embodiment of the present invention, a method formanufacturing an NMOS transistor and a PMOS transistor in a CMOStransistor will be described below by using the sectional views of FIGS.19 to 20, which show manufacturing steps.

The following structure is formed similarly to the steps described withthe drawings from (a) of FIG. 13 to (k) of FIG. 15 in theabove-described third embodiment.

Referring to (a) of FIG. 19, element isolation regions (not shown) areformed on the surface side of a silicon (Si) substrate 1 by using STI(Shallow Trench Isolation) or another method.

Subsequently, by an ion implantation method, impurities are introducedinto each of the NMOS transistor region and the PMOS transistor regionin order to carry out element isolation and threshold value adjustment.

Subsequently, a gate insulating film 17 having e.g. a high dielectric(High-k) insulating film is formed. This gate insulating film 17 isformed with a film thickness of e.g. about 1 nm to 3 nm by a filmdeposition method such as chemical vapor deposition (CVD) or atomiclayer deposition (ALD).

The above-described high dielectric insulating film is formed by using amaterial having a dielectric constant higher than that of silicondioxide. For example, it is formed by using a metal oxide, a metalsilicate, a metal oxynitride, or a nitrided metal silicate of one kindof metal selected from hafnium (Hf), lanthanum (La), aluminum (Al),zirconium (Zn), and tantalum (Ta). As one example of the material, anyof the following materials can be used: metal oxides such as hafniumoxide (HfO₂), aluminum oxide (Al₂O₃), and lanthanum oxide (La₂O₃); metaloxynitrides such as hafnium oxynitride (HfON) and aluminum oxynitride(AlON); metal silicates such as hafnium silicate (HfSiO); and nitridedmetal silicates such as nitrided hafnium silicate (HfSiON).

Furthermore, as one example, the above-described gate insulating film 17may be a component obtained by stacking the above-described highdielectric insulating film on a silicon-based insulating film such as asilicon dioxide film or a silicon nitride film.

Subsequently, a cap film 18 is formed on the gate insulating film 17.

This cap film 18 will serve as an etching stopper for preventing etchingdamage from entering the underlying gate insulating film 17 when a dummygate formed on the cap film 18 is removed in a later step. The cap film18 is formed of e.g. a titanium nitride (TiN) film. The above-describedcap film 18 is formed with a film thickness of e.g. about 3 nm to 10 nmby a film deposition method such as chemical vapor deposition (CVD) oratomic layer deposition (ALD).

Subsequently, a dummy gate electrode film (not shown) composed ofPoly-Si is deposited by e.g. a CVD method to a thickness of about 100 nmto 200 nm.

Next, by e.g. the CVD method, a SiN film that will serve as a hard maskis deposited on the dummy gate electrode film to a thickness of about 30nm to 100 nm.

Subsequently, a hard mask (not shown) is formed by processing theabove-described silicon nitride film through dry etching in which thisresist pattern is used as the mask.

Thereafter, the above-described resist pattern is removed, and then dryetching for the dummy gate electrode film is performed by using the hardmask as the mask, to thereby form a dummy gate electrode composed ofPoly-Si.

The etching of the dummy gate electrode film is performed in such a waythat the selection ratio with respect to the cap film 18 and the gateinsulating 17 of the high dielectric (High-k) insulating film isensured, to thereby prevent the silicon substrate 1 from being etched.

Thereafter, the above-described resist pattern is removed. By this posttreatment, the gate insulating film 17 covering the surface of thesilicon substrate 1 except for under the dummy gate electrode isremoved, so that the gate insulating film 17 is left only under thedummy gate electrode. The line width of the dummy gate electrode at thistime is several nanometers to several tens of nanometers at least.

Next, offset spacers 5 composed of e.g. silicon nitride (SiN) are formedto a thickness of 1 nm to 10 nm on the sidewalls of the gate insulatingfilm 17, the cap film 18, the dummy gate electrode 3, and the hard mask.

Subsequently, dummy sidewalls (not shown) composed of e.g. silicondioxide (SiO₂) are formed on both the sides of the gate insulating film17, the cap film 18, the dummy gate electrode, and the hard mask, forwhich the offset spacers 5 have been provided.

Here, the dummy sidewalls will be removed by etching selectively withrespect to the offset spacers 5 in a later step. Therefore, it ispreferable that the dummy sidewalls be formed by using a material whichcan take etching selection ratio with respect to the material of theoffset spacers 5.

Next, recess etching for partially removing the silicon substrate 1 isperformed by using the hard mask on the dummy gate electrode and thedummy sidewalls as the etching mask, to thereby form recess regions 7with a depth of about 50 nm to 100 nm.

Through this recess etching, only the recess regions 7 for one of anNMOS and PMOS are formed in some cases, and the recess regions 7 aresequentially formed for both an NMOS and PMOS in other cases.

At this time, resist patterning is carried out on the NMOS transistorside at the time of the formation of the mixed crystal layer for thePMOS transistor, such as silicon germanium (SiGe), and resist patterningis carried out on the PMOS transistor side at the time of the formationof the mixed crystal layer for the NMOS transistor, such as siliconcarbide (SiC), and the protective film of silicon dioxide (SiO₂) usedfor the above-described anti-channeling is left.

Next, on the surfaces of the recess regions 7, i.e., on the surface ofthe partially etched part of the silicon substrate 1, mixed crystallayers 8 (8 p) composed of silicon (Si) and atoms having a latticeconstant different from that of silicon (Si) are epitaxially grown.

At this time, in the PMOS transistor side, a silicon germanium(hereinafter referred to as SiGe) layer composed of silicon (Si) andgermanium (Ge) having a lattice constant larger than that of silicon(Si) is epitaxially grown as the mixed crystal layers 8.

Thereby, the region in the silicon substrate 1 between the mixed crystallayers 8 p and directly beneath the dummy gate electrode will functionas a channel region, and compressive stress is applied to the channelregion from the mixed crystal layers 8 p.

On the other hand, in an NMOS transistor side, a silicon carbide (SiC)layer composed of silicon (Si) and carbon (C) having a lattice constantsmaller than that of silicon (Si) is epitaxially grown as the mixedcrystal layers 8 (8 n). Simultaneously with the epitaxial growth of theSiC layer, an n-type impurity such as arsenic (As) or phosphorous (P) isintroduced with a concentration of 1×10¹⁹/cm³ to 5×10²⁰/cm³.

The C concentration in the SiC layer of the mixed crystal layers 8 n isset to a value in a concentration range of 0.5 atm % to 1.5 atm %, inorder to prevent crystal defects due to the existence of a highconcentration of carbon (C) in the silicon carbide layer and effectivelyapply stress to the channel region. This concentration is set toconcentration lower than the germanium (Ge) concentration that has beenreported to be the optimum generally. This is a merit attributed to thestress enhancement effect due to the damascene gate structure, whichwill be described later.

Here, for effective stress application to the channel region, it ispreferable that the mixed crystal layers 8 be so formed as to protrudefrom the surface of the Si substrate 1.

Furthermore, the Ge concentration in the SiGe layer of the mixed crystallayers 8 p is set to a value in a concentration range of 15 atm % to 20atm %, in order to prevent crystal defects due to the existence of ahigh concentration of Ge in the SiGe layer and effectively apply stressto the channel region.

Next, the dummy sidewalls are removed by e.g. wet etching to therebyexpose the surfaces of the offset spacers 5 and the Si substrate 1.

Subsequently, a p-type impurity such as boron ions (B⁺) or indium ions(In⁺) is introduced into the PMOS transistor side by e.g. an ionimplantation method, to thereby form shallow-junction extension regions9 (9 p) on the surface side of the silicon substrate 1 on both the sidesof the offset spacers 5.

At this time, as the condition of the ion implantation, the implantationis performed with implantation energy of 100 eV to 300 eV and a dosageof 5×10¹⁴/cm² to 2×10¹⁵/cm², so that a shallow junction is formed.

On the other hand, arsenic ions (As⁺) or phosphorous ions (P⁺) areimplanted also into the NMOS transistor side e.g. with implantationenergy of 100 eV to 300 eV and a dosage of 5×10¹⁴/cm² to 2×10¹⁵/cm², sothat a shallow junction is formed.

It is to be noted that the ion implantation into the respective elementregions is performed in such a way that the NMOS transistor region iscovered by a protective film such as resist in ion implantation into thePMOS transistor region, and is performed in such a way that the PMOStransistor region is covered by a protective film such as resist in ionimplantation into the NMOS transistor region.

Thereafter, sidewalls 10 composed of e.g. SiN are formed again on boththe sides of the offset spacers 5.

Subsequently, by an ion implantation method, impurities in matching withthe conductivity types of the respective mixed crystal layers 8 areintroduced into the surfaces of the respective mixed crystal layers 8with use of the hard mask 4 and the sidewalls 10 as the mask. This ionimplantation is performed in order to reduce the contact resistance of asilicide layer that will be formed on the surfaces of the mixed crystallayers 8 in a later step.

Subsequently, a refractory metal film (not shown) is formed by e.g.sputtering across the entire surface of the silicon substrate 1,including on the mixed crystal layers 8, in such a manner as to coverthe dummy gate electrode 3, for which the hard mask 4 and the sidewalls10 have been provided. Here, as the refractory metal, cobalt (Co),nickel (Ni), platinum (Pt), or a compound of these metals is used.

Subsequently, the silicon substrate 1 is heated to thereby turn thesurface side of the mixed crystal layers 8 into a silicide, so thatsilicide layers 11 are formed.

Thereafter, the unreacted refractory metal film remaining on the elementisolation regions (not shown) and the sidewalls 10 is selectivelyremoved.

Subsequently, an interlayer insulating film 12 composed of e.g. silicondioxide (SiO₂) is formed across the entire surface of the siliconsubstrate 1, including on the silicide layers 11, in such a manner as tocover the dummy gate electrode, for which the hard mask and thesidewalls 10 have been provided.

At this time, in some cases, a liner silicon nitride (SiN) film forcontact etching stop is formed and silicon dioxide (SiO₂) or the like isdeposited thereon in a stacked manner to thereby form theabove-described interlayer insulating film 12.

Thereafter, the interlayer insulating film 12 and the hard mask areremoved by a CMP method until the surface of the dummy gate electrode isexposed.

Subsequently, the dummy gate electrode is selectively removed by dryetching, to thereby form a recess 13. At this time, the cap film 18 atthe bottom of the recess 13 serves as the etching stopper, and thusetching damage does not enter the gate insulating film 17.

For example, in the above-described dry etching, a mixture gas ofhydrogen bromide (HBr) and oxygen (O₂) is used as the etching gas.Thereby, it is avoided in the PMOS transistor that the stress appliedfrom the mixed crystal layers 8 to the channel region Ch directlybeneath the dummy gate electrode is suppressed by counteraction from thedummy gate electrode. Thus, the compressive stress to the channel regionCh is increased. Also in the NMOS transistor, the tensile stress to thechannel region is increased similarly.

Subsequently, heat treatment is performed for the Si substrate 1, fromwhich the dummy gate electrode has been removed, at a temperature of500° C. to 700° C. for ten seconds to several minutes.

This further increases the stress to the channel region Ch by the mixedcrystal layer 8. Furthermore, this heat treatment can also offer theeffect to recover the damage to the high dielectric (High-k) insulatingfilm.

In the above-described heat treatment, the effect to reduce the leakageis small with a temperature lower than 500° C. In contrast, atemperature higher than 700° C. causes crystallization and thus makes itdifficult to achieve the reliability. Therefore, the treatmenttemperature is set to the above-described temperature.

Subsequently, as shown in (b) of FIG. 19, a metal film 20 to be reactedwith the above-described cap film 18 is formed at least on the bottom ofthe above-described recess 13. This metal film 20 is formed by usinge.g. a metal such as aluminum (Al), titanium (Ti), copper (Cu), orlanthanum (La). As the film deposition method therefor, e.g. a chemicalvapor deposition (CVD) method or an atomic layer deposition (ALD) methodcan be used.

Subsequently, as shown in (c) of FIG. 20, a resist mask 32 is so formedas to cover the NMOS transistor side. This resist mask 32 is formed bynormal resist application technique and lithography technique.

Subsequently, the above-described metal film 20 on the above-describedPMOS transistor side (see above-described (b) of FIG. 19) is removed. Inetching of this metal film 20, the metal film 20 is selectively removedby wet etching or dry etching that gives little etching damage to theunderlying cap film 18, to thereby leave the cap film 18 at the bottomof the recess 13 on the above-described PMOS transistor side.

Subsequently, as shown in (d) of FIG. 20, a film 22 that controls thework function is formed by reacting the above-described metal film 20with the above-described cap film 18 (see above-described (b) of FIG.19). For example, if titanium nitride is used as the above-described capfilm and any one of aluminum, copper, and lanthanum is used as theabove-described metal film 20, the above-described heat treatment isperformed in an inactive atmosphere like a nitrogen gas or a noble gasat a temperature of 300° C. to 500° C., for example.

Because the gate insulating film 17 having the high dielectricinsulating film and the cap film 18 are formed of a metal-basedmaterial, the heat treatment needs to be performed at a temperatureequal to or lower than 500° C. so that the gate insulating film 17 willnot react. Furthermore, a temperature lower than 300° C. leads to lowreactivity between the metal film 20 and the cap film 18, and thereforethe heat treatment is performed at a temperature equal to or higher than300° C.

Subsequently, a gate electrode 15 is formed inside the recess 13similarly to the step described with the above-described (d) of FIG. 18.In this manner, in the NMOS transistor, the gate electrode 15 is formedover the gate insulating film 17 in the recess 13 with the intermediaryof the film 22 that controls the work function. Furthermore, in the PMOStransistor, the gate electrode 15 is formed over the gate insulatingfilm 17 and the cap film 18 in the recess 13.

It is preferable to form an adhesion layer (not shown) when theabove-described gate electrode 15 is formed. For example, if tungsten(W) is used as the gate electrode 15, a titanium nitride (TiN) film isused as the adhesion layer. If aluminum (Al) is used as the gateelectrode 15, a titanium (Ti) film is used as the adhesion layer. Ifcopper is used as the gate electrode 15, a tantalum (Ta) film is used asthe adhesion layer.

Through the above-described steps, a CMOSFET is formed.

Thereafter, an interlayer insulating film is further formed on theinterlayer insulating film 12, including on the gate electrode 15, andcontacts and metal interconnects are formed, so that the semiconductordevice is fabricated, although not shown in the drawings.

According to such a method for manufacturing a semiconductor device anda semiconductor device obtained by this method, the recess 13 is formedby removing the dummy gate electrode. Thus, it is avoided that stressapplied from the mixed crystal layers 8 to the channel region Chdirectly beneath the dummy gate electrode is suppressed by counteractionfrom the above-described dummy gate electrode. Thereafter, the gateelectrode 15 is so formed on the gate insulating film 14 in the recess13 that the stress state is kept. This allows effective stressapplication to the above-described channel region Ch, and hence canstrain the channel region Ch to thereby enhance the carrier mobility.

In addition, this effective stress application to the channel region Chmakes it possible to decrease the concentration of the atoms having alattice constant different from that of silicon (Si) in the mixedcrystal layers 8. This feature can surely prevent crystal defectsattributed to the existence of a high concentration of theabove-described atoms in the mixed crystal layers 8.

In addition, due to the provision of the work function control film 22,the work functions of the NMOS transistors are controlled, which allowsfurther enhancement in the carrier mobility.

Consequently, characteristics of the transistor can be enhanced.

What is claimed is:
 1. A semiconductor device comprising: a siliconsubstrate; a gate electrode over the silicon substrate; a gateinsulating film between the gate electrode and the silicon substrate,the gate insulating film at least including hafnium; as viewed in crosssection, an offset spacer between a sidewall film and the gateelectrode; a source/drain region in the substrate, the source/drainregion having a lattice constant different from a lattice constant ofsilicon substrate; a work function control film between the gateinsulating film and the gate electrode; as viewed in the cross section,a first insulating film on both of oppositely facing sides of the gateelectrode; and as viewed in the cross section, a second insulating filmcontacting at least a portion of a top surface of the gate electrode. 2.The semiconductor device of claim 1, wherein the second insulating filmis above the first insulating film, and the first insulting film doesnot contact the top surface of the gate electrode.
 3. The semiconductordevice of claim 1, wherein the sidewall film is between the gateelectrode and the first insulating film.
 4. The semiconductor device ofclaim 3, wherein the semiconductor device is a p-type field effecttransistor, and the source/drain region at least includes silicon andgermanium.
 5. The semiconductor device of claim 1, wherein the firstinsulating film covers the sidewall film.
 6. The semiconductor device ofclaim 1, wherein the work function control film comprises a metalsilicon or a metal nitride.
 7. The semiconductor device of claim 1,wherein the work function control film is in contact with the offsetspacer.
 8. The semiconductor device of claim 1, wherein, the gateinsulating film is only between the gate electrode and the siliconsubstrate.
 9. The semiconductor device of claim 1 further comprising asilicide layer on a surface of the source/drain region.
 10. Thesemiconductor device of claim 9, wherein the first insulating film is onthe silicide layer.
 11. The semiconductor device of claim 1, wherein thegate electrode comprises at least one metal material.
 12. Thesemiconductor device of claim 1 further comprising a shallow-junctionextension region on the silicon substrate that extends from thesource/drain region to a channel region underneath the gate electrode.13. The semiconductor device of claim 1 further comprising asilicon-based insulating film between the gate insulating film and thesilicon substrate.
 14. The semiconductor device of claim 1 furthercomprising a cap film that is only between the gate electrode and thework function control film.